So where are young teens going online if not to Facebook?
Sites, like Instagram, which is owned by Facebook, Snapchat and WeChat are gaining a following among younger users who want to communicate, follow their favorite celebrities and sports stars and share images.
Rob Enderle, an analyst with the Enderle Group, said Facebook needs to get ahead of this issue now before it gets worse.
"It's a very big problem," he added. "New trends like social networking are largely driven by youth. If they abandon the technology and move on, Facebook bleeds growth potential and it is far more likely to drop into decline."
However, Dan Olds, an analyst with The Gabriel Consulting Group, said he doesn't see this as a big worry for Facebook, since teenagers are just looking around and trying out new apps and new networks.
"I don't think that kids are losing interest in social networking at all," he said. "It's more that they might be using different vehicles, like Instagram, which is owned by Facebook. Teens were the early adopters with Facebook and it's natural that some will use other platforms when they suddenly see mom, dad, and their old Aunt Milly start friending them on Facebook. When the adults arrive, it definitely kills the 'cool factor' for at least some teens."
The fact that teenagers are increasingly using Instagram means that Facebook CEO Mark Zuckerberg made a pretty savvy move when the company bought the start-up last year.
"I think Facebook needs to make sure that at least one of their brands, like Instagram or whatever, appeals to the youngest crowd," said Olds. "But not all of their brands need to do that."
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