That said, 88% of US teens still continue to use Facebook, and that number rises among all age groups over age 25. In general, Facebook user numbers still continue to grow in all age groups, especially outside the US, so you won't see a panic in the FB boardroom any time soon.
In fact, teens that leave Facebook tend to go to Instagram instead. You know who owns Instagram? Facebook, of course, so the service is losing teens basically to itself.
What this means to band or artist is that if your fanbase is comprised mostly of teens, then Instagram should definitely be part of your social media promotion mix. But don't forget Facebook, since a great many teens still do check it out, especially outside the US.