Cashing in on the social chatter surrounding TV programming has been a dream of networks and Madison Avenue for the past few years. They pounced each time mobile "second-screen" apps like Viggle and GetGlue came along and promised deeper engagement with viewers, but struggled to assemble large enough "social TV" audiences to make deals worth the effort.

So it was no surprise that everyone wanted in when Twitter, the most powerful platform for social TV conversations, unveiled "Instant Replay" in December 2012, encouraging media companies to promote video tweets prefaced with brief clips from sponsors. The product, which evolved into Twitter Amplify, now boasts more than 80 media partners in 10 countries, including sports leagues and all four major broadcasters.

But as the initial allure begins to fade, Amplify customers say Twitter has to evolve its strategy or risk becoming just another phase in the quest to make money on social TV. Amplify may work for sports and live events like awards shows, but executives who have tried it on other programs say it doesn't have the same results. "Advertisers are finding that Twitter as an always-on property is still trying to find its way," said Ron Amram, senior media director-marketing, Heineken. "In the moment, in real time, it is fantastic. Now it's about looking beyond sports and live events. The next wave of this is how do you use Amplify with everyday TV schedules?"

Marketers have also chafed at the rigid format. And networks aren't enthusiastic about sharing money with Twitter if it comes out of TV budgets -- as has sometimes proved the case.

For Twitter, Amplify is part of a broader strategy to court TV networks and major TV advertisers, positioning itself as a partner instead of a foe. But it's facing increased pressure as social media platforms including Facebook, Instagram and Tumblr ramp up their own efforts to work with media companies and advertisers. And as Twitter's user growth slows down, successfully tapping TV ad budgets will become even more important.

Epic moments
When Rafael Nadal and Novak Djokovic fought out an epic 54-shot rally in the final match of the U.S. Open tennis tournament last September, Heineken and the United States Tennis Association used Amplify to post and promote a replay with a few seconds of branded video before it. It was retweeted 1,500 times; Mr. Amram said for most brands, 100 retweets is respectable for a standard promoted tweet.

In total the campaign generated 12 million impressions and 200,000 retweets, favorites, clicks and follows, across 124 tweets, and Heineken added 2,300 Twitter followers. The brewer plans to use Amplify again during this year's U.S. Open.

The National Football League is talking with Twitter to renew and expand its Amplify. Last season it only amplified content around "Thursday Night Football," but it's now looking to make the platform accessible for all games, said Vishal Shah, VP-digital media business development at the NFL.

Amplify can win outside of sports too. Pepsi found success with its first Amplify campaign, during MTV's 2013 Video Music Awards, adding 9,000 Twitter followers that were relevant to the show, said Chad Stubbs, senior director, Pepsi Media. And 98% of the people who started playing the videos released in Amplify posts watched the whole thing, he added. Pepsi will use Amplify during the next VMAs. It's also run Amplify campaigns with CBS during the Grammy Awards; it's in conversations about repeating that effort.

Jeff Lucas, head of sales, music and entertainment at MTV parent Viacom, called Amplify a natural fit with the company's audience, which skews younger and is heavily active on social media. "Our clients love it," Mr. Lucas said. "It allows them to have more content in real time and more touch point to the consumer. We have not had trouble finding sponsors."

Scripted struggle
But questions began as soon as TV networks began trying the Amplify formula of highlight videos on other programming beyond sports, like scripted dramas and talk shows. Live events get people talking at the same time, and you want to see an incredible athletic feat more than once, a snappy line of scripted dialog just doesn't grip people en masse the same way.

"In the non-sports world there's been a hard time justifying Amplify to sponsors," said one TV executive that's tried it and doesn't plan to aggressively pursue more campaigns.

Many of the networks and advertisers that have tried Amplify campaigns around episodic TV shows haven't come back for more.

A&E Networks was an early Amplify partner, signing up to try the product as it rolled out in its current form in May 2013. But the company has run just one campaign, around "Duck Dynasty." An A&E Networks spokeswoman declined to discuss on the status of the company's Amplify deal.

American Express made a meaningful investment in Amplify last November, when it agreed to a season-long deal with Fox to co-brand clips from shows like "Glee," "The Mindy Project" and "Bones."

"We are pleased with initial results and performance," said Jill Toscano, VP-U.S. Media, American Express, noting that Amplify improved engagement between 50% and 60% over promoted tweets that weren't part of the program.

Still, American Express has not renewed the deal. Ms. Toscano said the company will consider future Amplify partnerships.

CBS has taken some of the biggest swings thus far, completing just under a dozen or so campaigns for "60 Minutes," sports events and its mystery drama "Elementary." In what was dubbed one of the most comprehensive Amplify deals, CBS struck a deal in September 2013 that originally promised advertisers the ability to sponsor clips from 42 of its shows, with ideas like Amplify versions of "60 Minutes" called "60 Minutes in 60 Seconds."

Although the network is currently out in the marketplace seeking sponsors for a new batch of ideas, there are currently none slated to run, said Marc DeBevoise, senior VP-general manager of CBS Interactive, admitting some proposals didn't resonate with advertisers.

Mr. DeBevoise said it's still too early in the partnership to determine how big Amplify can get, "but advertisers are happy," and CBS is in renewal conversations with more than one prior sponsor. Still, he said, Amplify "will only work for the right brand at the right time."

Glenn Brown, who leads Twitter Amplify, admits content that doesn't air in real time doesn't perform as well on Twitter, but said the company is committed to working with non-sports partners "to figure out what second-screen is to them."

"The entertainment side is the biggest area for growth for Amplify," Mr. Brown added.

To that end, Twitter has been expanding its suite of products designed to simplify the process of programming the second-screen. The company recently agreed to buy SnappyTV, which allows users to quickly edit and share clips from TV.

"Broadcasters can identify key tweetable moments and when that piece of content airs on TV can immediately convert it with SnappyTV into a short video or gif," Mr. Brown said.

And the acquisition last fall of MoPub, a mobile ad exchange, is expected to improve Twitter's ad targeting capabilities. The company has also purchased two companies that track social TV analytics and last month began supporting gifs.

Viacom, which has also tried Amplify for social-media-friendly shows such as Comedy Central's "The Colbert Report" and "Tosh.0," admits that live events have driven more social traffic, but it hasn't given up on taped entertainment programming. The company is working on developing Amplify campaigns for MTV's "Teen Wolf" to run over the course of several episodes or possibly the entire season.

It may help if Amplify can expand beyond its usual format. "The Amplify product is limited to video clips with pre-roll ads," a second TV executive said. "We are currently in conversations with Twitter regarding the potential to go beyond that. Amplify was a great way to start the conversation, but it needs to evolve from there."

Mr. Brown said that from the get-go Amplify has always been more than just video. He pointed to Major League Baseball using photos during the World Series and the Twitter Mirror, which allowed celebrities take selfies sponsored by Samsung during the Academy Awards.

And for "The Colbert Report," Viacom and T-Mobile decided to tweet a clip with an in-show brand integration instead of the pre-roll.

Among marketers, Coca-Cola is looking for greater flexibility in choosing video highlights and leeway to look outside the pre-selected packages that are currently offered, a company spokeswoman said in an email, calling for a clearer understanding of rights and how content can be used.

Who pays what
There are also questions around marketers' costs, which have varied widely among TV networks participating. While Coca-Cola saw an increase in consumer engagement on Twitter with Amplify campaigns around live events like 2014 NCAA March Madness on CBS and Turner Broadcasting, it wants greater transparency and standardization in pricing models from broadcast partners and Twitter alike.

Costs are highly inconsistent across broadcast programming offerings, the Coca-Cola spokeswoman said.

Some TV network executives have begun to wonder, meanwhile, why they should share ad revenue with Twitter.

"Initially we were excited about Amplify as a way to get incremental revenue. We bought into the premise," the first TV executive said. "But when we went into the marketplace we were surprised sponsors didn't find value in it and they didn't want to spend extra. Some suggested reducing their buy with the network to give portion to Twitter, which of course didn't sit well for us."

"The value proposition is tricky," a media buyer agreed. "Advertisers need to pay both the networks and Twitter. It is a nice chunk of money for something advertisers are not convinced has value."

While pricing varies by network, a second media buyer said agreements typically start at six figures and deals with sports affiliates can run seven figures.

Mr. Brown declined to disclose terms of the deals. TV networks are typically charged with selling pre-roll videos, while Twitter offers its ad products, like promoted tweets. Advertisers only pay when there's an interaction with the tweet.

Of course, marketers don't need to use Amplify to associate themselves with TV content; they can just as easily work directly with the networks to push out relevant content around programming. But CBS' Mr. DeBevoise said Twitter's access to user data allows them to be much more targeted and efficient then if Twitter were not in the picture.

Through Amplify, marketers can reach not only people tweeting in the moment, but also target anyone else who might be interested in the content, follower or not, Mr. Brown said.

Twitter is forecasting revenue as high as $1.25 billion this year, nearly double its revenue in 2013. And a few analysts have improved their outlook on Twitter recently, although that's largely due to revenue potential of MoPub. What's unclear is how much of Twitter's revenue is derived from Amplify. Mr. Brown declined to disclose revenue figures.

It's likely negligible, according to an analyst. "It's probably a rounding error, if anything," said Brian Wieser, analyst at Pivotal Research Group. "It's more important on a strategic level than an operation level."

What Amplify has done, Mr. Wieser said, is given Twitter a seat at the table with senior marketers that it otherwise might not have.