ISSUE: Find a way to attract TV-avoiding teens to Subway.

SOLUTION: A custom-made digital video series featuring high schoolers working their first after-school job at the sandwich chain.

While many fast-food chains obsess about millennials, Subway's sore point has been teens.

The demographic has eluded the chain, said Karie Ford, VP-media, in part because teens are watching less live TV and spending more time on Hulu and Netflix. Not only are teens "fickle and unpredictable," said Ms. Ford, they are "put off if you're directly advertising to them. We knew we needed something unique and breakthrough ... we wanted to do something long-lasting, so we felt like a series was the best route."

Subway did its homework, trying to discover what was meaningful to teenagers. "We looked at a lot of firsts, and when we looked at rites of passage, one piece that stood out was that first job," said Ms. Ford.

And so "The 4 to 9ers" was born.

Subway enlisted Los Angeles-based Content & Co., which develops, produces and distributes content, for a show about teenage Subway employees who work there after school. "The 4 to 9ers" follows a typical sitcom narrative: it chronicles the teens' triumphs and tribulations and their annoying parents.

The six 10-minute episodes first aired on Hulu in late 2012. Content & Co. supplemented the series with additional content by creating fan channels on YouTube, Instagram, Facebook and Twitter, where additional behind-the-scenes videos lived and fans could share their first-job stories. Hulu featured it as a Spotlight Series, which gave "The 4 to 9ers" special attention on the Hulu home page.

It was such a hit that a second season was ordered in 2013. "The 4 to 9ers" became the No. 1 scripted short comedy on Hulu, generating 18 million views totaling 400,000 hours of viewing time, said Ms. Ford. She was reluctant to give an exact sales figure for the teen demographic, but said "when we looked at our share, we saw a good uptick in momentum. We had double-digit growth on a percentage basis." The writing for the third season of "The 4 to 9ers" is now underway, with the intention that it will be a long-running show.

Thanks to the success of "The 4 to 9ers," Subway is working with Content & Co. to launch in June "Summer with Cimorelli," a branded series about the Cimorelli sisters, six siblings who got attention by posting videos featuring a cappella versions of pop songs on YouTube. The company also staged a large brand integration in Hulu's "My Side of the Sky," a documentary-style reality series about students, coaches and teachers at Windells Academy, a school in Mt. Hood, Ore.