The Duff,” a low-budget high school comedy from CBS Films and Lionsgate, shows that Twitter, YouTube and other social-media platforms can be deployed to get 21st century teenagers interested in something as comparatively old fashioned as a movie.

The film opened to $10.8 million, a respectable number for a production that cost $8.5 million to make and lacks any big-name actors. The relative success of the picture is a testament to cost-efficient outreach to a group of female moviegoers who like communicating in 140 characters and are often ignored by mainstream movie studios — girls between the ages of 11 and 18. It’s the same demographic that helped turn “The Fault in Our Stars” and “Twilight” into major hits and one that some Hollywood players think could become a reliable block of ticket buyers.

“I know that this group goes to the movies as a social function,” said Terry Press, president of CBS Films. “They go in packs on Friday nights, and they’re invested in the social aspect of going to a movie theater in a way that you do not find with their male counterparts.”

“Social media is how this particular audience lives and breathes,” she added. “It is the swiftest and most economical way to reach them.”

“The Duff” team exploited these platforms for something akin to an extended crowdsourcing session, sending posters, trailers and other promotional materials to Internet hubs and then picking through the data to strengthen their pitch. The studios used fans’ reactions to tweak their TV spots and to gather information on their core audience. To raise awareness, the film’s backers also created a contest in conjunction with AMC Theatres allowing fans to enter their photos for a chance to be a part of the film’s final poster.

Digital promotion has always held out the tantalizing possibility of enabling studios to eschew costly print and television spots in favor of cheaper Web ads. However, CBS Films’ team argues that there needs to be a place for some television promotion. Spots for “The Duff” were often paired with episodes of shows such as “Pretty Little Liars,” “The Flash” (in which star Robbie Amell has a recurring guest role) or “Vampire Diaries” that are popular with that age group, with members of the movie’s youthful cast taking to Twitter to plug the spots.

“My biggest rule is to make something for somebody,” said Press. “I knew that this could be an event for this audience, and I didn’t want to spend one dime chasing a boy that was never going to show up.”

The filmmakers tried to exploit the popularity of Kody Keplinger’s young adult novel of the same name and to find the universal elements of its story of a teenager who is deemed a “DUFF” — “Designated Ugly Fat Friend.” Everyone, the thinking went, can relate to some high school horror stories. The campaign drew on the film’s anti-bullying message to partner with advocacy groups such as Mean Stinks and I Am That Girl as a way to broaden its audience and raise awareness. Throughout production and in the months leading up to its February release, “The Duff” team worked to build up its social-media cred, casting YouTube stars such as Alex Wassabi and Blair Fowler in cameos.

Screenings were another key element to “The Duff’s” distribution plan, with CBS Films and Lionsgate offering hundreds of chances for audiences to see the film early, often with cast members on hand for photos with fans.

Partnering with Lionsgate, CBS Films’ distribution partner, proved invaluable, because the studio knew the audience intimately from its work on “The Hunger Games” and “Divergent” series, films that also appealed to girls.

Some pictures try to be what are called four-quarant movies, offering something for everyone. “The Duff” never got greedy. Seventy percent of its open weekend crowd was under the age of 24, an exercise in preaching to the converted that impressed analysts.

“They always knew who they were trying to reach and they didn’t try to reach anyone else,” said Kevin Goetz, founder and chief executive officer of research firm Screen Engine/ASI. “You can apply this to so many movies so it becomes a whole new template for niche films.”