"We're supportive of these websites growing, and the websites integrated with Facebook are more social because of it," said Malorie Lucich, communications manager for Facebook.
Facing mounting investor scrutiny after its disappointing IPO, Facebook is under pressure to report increased growth and revenue to Wall Street.
But Facebook, which claims more than 900 million members, had 158 million unique visitors to its site in April, according to researcher ComScore, up just 5% from a year ago. That compares with year-over-year growth rates of 89% in April 2010.
More than eight years after Facebook's inception, its mass appeal has drawn older crowds who add their kids as Facebook friends. That development could be tarnishing the site's "cool factor" in the eyes of teens, said Jake Katz, chief architect at YPulse.
There are other reasons teens are divvying up their digital presence. It assures them more privacy, as well as new popularity among a smaller audience. Instagram, for example, features users' photos on its "Popular" page.
"There's a new flavor of gratification," that Facebook doesn't have, Katz said.
To meet rising mobile interests, where many teens surf the Internet and chat, the social giant has made strides to make its mobile app a crucial part of Facebook.
Facebook has sliced site functions into separate mobile apps such as Facebook Messenger and Facebook Pictures, a move that could appeal to teens, as online identities spread across multiple sites, Katz said.
Also, the social network is testing ways to allow those under 13, currently prohibited, to participate with parental supervision.