Think you're hip like a teenager? If you spend a lot of time on Facebook, think again. According to a report from market research firm eMarketer, teens are leaving Facebook faster than expected as older users embrace the social network.

The firm predicts that Facebook will lose 2 million users ages 24 and younger in 2018. "This year, for the first time, less than half of US internet users ages 12 to 17 will use Facebook via any device at least once per month," eMarketer wrote in a blog post.

Facebook is still growing, but "older age groups" are driving that trend, eMarketer wrote. This year, Facebook is expected to reach 169.5 million US users, up less than 1 percent from 2017. But at the same time, the number of US Facebook users age 11 and younger is expected to decline by 9.3 percent, the firm predicted, while users ages 12 to 17 decrease 5.6 percent and users between 18 and 24 drop 5.8 percent.

Facebook recently started targeting younger audiences with Messenger Kids, its first app built specifically for children. But that app has drawn criticism from child advocates and experts, who argue it will "undermine children's healthy development."

Facebook owns Instagram, "but not all of those users are migrating to Instagram," eMarketer wrote. The photo-sharing service will add 1.6 million users ages 24 and younger this year, while Instagram's total user base is expected to increase 13.1 percent to 104.7 million in 2018, the firm predicts.

Facebook declined to comment on the report. Predictions about the social network's demise are not new, though. In 2014, for example, Princeton University researchers predicted that Facebook would lose 80 percent of its peak user base between 2015 and 2017. We're not quite there yet, but Facebook did recently change its News Feed algorithm to feature more posts from friends and family rather than news stories and viral videos, which it admitted has decreased time spent on the service.

Rival Snapchat, which has seen Facebook crib many of its features, is forecast to grow 9.3 percent to 86.5 million. "Snapchat could eventually experience more growth in older age groups, since it's redesigning its platform to be easier to use," eMarketer principal analyst Debra Aho Williamson said in a statement. "The question will be whether younger users will still find Snapchat cool if more of their parents and grandparents are on it. That's the predicament Facebook is in."

Early reactions about the Snapchat update have been largely negative, however. Following the redesign's rollout in the US, more than 30 petitions were launched on Change.org in a single day, which asked Snap to change the app back to the way it was before.