Cord-cutters, who are driving ad dollars away from TV and toward digital media, are also pushing more marketers into the gaming arena. Video games and electronic sports, or e-sports, are emerging as a viable way to reach tech-savvy millennials, particularly males who aren't consuming traditional media and sports.

Over the past two years, major brands such as Coca-Cola, HTC, Geico and Procter & Gamble have entered the gaming space by sponsoring e-sports teams and tournaments, running experiential pushes at events or creating interactive experiences on the gaming platform Twitch. Others, like T-Mobile and Samsung, are also courting the gaming industry, dabbling with sponsorships or teaming up with gaming companies to better engage audiences.

The environment is still largely untapped, providing a major opportunity for advertisers.

"It's pretty much uncluttered when it comes to nonendemic brands," said Deric Ortiz, founder of the events firm One Nation of Gamers and a gaming consultant who works with Geico and T-Mobile. "There's room to play and do some really cool stuff."

Brands like Taco Bell and Pizza Hut have taken up posts at major gaming events like Valve's Dota 2 tournaments and backed teams, while others like Red Bull have hosted their own events.

"The brands that are progressive and speak to youths are the first ones to come," said Andy Swanson, VP of e-sports and events at Twitch, which was acquired by Amazon last year. Others then follow.

A majority of the requests for proposals that Twitch receives from brands are from nongaming advertisers, including movie studios, consumer packaged goods, beverage brands and quick-service restaurant chains, although it also gets a lot of requests from gaming companies, Mr. Swanson said.

The industry, especially game developers, is selective about working with brands because it wants to preserve e-sports' authenticity. It does not want to end up like Nascar with logos plastered all over their events.

"We want to make sure we're super deliberate in our approach to working with sponsors," said Dustin Beck, VP of e-sports at publisher Riot Games, which has worked with major brands like Coca-Cola, HBO and American Express to help go beyond basic sponsorships and ad buys. "It's challenging from a creative perspective to make sure these brands have a great initial entrance into the scene."

HTC, which began sponsoring three U.S. e-sports teams earlier this year, has been leveraging those relationships to get closer to fans. The mobile phone manufacturer has a YouTube channel with original content starring its top gamers. It also holds fan contests in which winners get to play a game of their choosing with their favorite players, as well as a few HTC employees.

"One thing about e-sports that makes it a little bit harder for companies to get into is that you really have to be integrated among the community," said Walter Wang, e-sports project manager at HTC. "You have to interact with [gamers] in a real way."

One of the most notable examples is P&G's recent push for its Old Spice brand on Twitch. The CPG brand was inspired by a livestream on the platform where viewers can control Pokemon characters by entering commands into Twitch's chat feature. For Old Spice, P&G gave Twitch users control over a real person's life for three days while he camped in the woods. Dubbed "Nature Man," he was told where to walk and what to do through a selection of commands. The effort garnered more than 2.3 million views on Twitch.

"It was hugely successful," said Twitch's Mr. Swanson, noting the company has an ad sales team that helps big media buyers create custom activations like these. "We loved that idea of the crowd controlling him."

P&G also tapped Twitch broadcaster and gamer "itmeJP" to promote its Gillette brand. The popular gamer, known for his prominent beard, shaved using a Gillette razor while playing the "Marvel Heroes" game in a push tied to Marvel's "Avengers: Age of Ultron" film. And NBC Universal's USA Network "hacked" Twitch's E3 livestream in June. The three-day effort for the new show "Mr. Robot" teased users with messages from a fictional society from the program that offered to erase consumer debt. The network gave away $100,000 in payouts during the push.

Still, e-sports is far from becoming a full-fledged advertising platform on par with global sports like soccer and national pastimes such as football. But the category is growing fast.

"Every year of experience we get under our belt, conversations with various sponsors and advertisers become increasingly easier," said Riot Games' Mr. Beck, who added that a huge part of his job is educating marketers on the business and its audience. "Those conversations are becoming easier to have as our numbers become bigger and people start to understand what e-sports is."