I've heard it a billion times that teens aren't using Facebook. But who cares? I just don't see any evidence that this heralds the end of Facebook.
It's not necessarily any more meaningful than "people ages 65-70 don't use Facebook". It's a small percentage of the population. And there's no indication that teens are using something else that will replace Facebook when they're in their 20's and 30's -- you can't organize parties on Instagram or Snapchat. Every indication is that teens get onto Facebook once they stop being teens, correct me if I'm wrong.
Can we stop talking about this ineffable "cool" factor, until there's any kind of evidence that it is actually necessary for Facebook's continued success? I mean, I don't remember Facebook ever being cool. It's always been pretty drab, a pretty bland boring blue, with an interface much like an OS. But it just works better than the alternatives, and keeps working better. Why people are suddenly constantly talking about this "lack of cool" is beyond me.