Young people avoid the timeline because it is for old people and mostly public. Facebook knows how young people use Facebook. It is in ways you don't see. It's Messenger and private groups
Also anecdotal, but this past Thanksgiving I got into a chat with two nieces and a couple of their friends, all in the late-teen range.
They're really concerned about the amount of information these big data stores have on them.
They're worried even more that there is a government snoop checking in on them or another unknown.
Personally, I have gotten more and more leery of putting data online. I deleted my Facebook 7 years ago. Twitter is strictly read-only for me. I share kid pics directly with family via private storage I control.
Really needs to be a peer-2-peer suite of "social" tools that cut out middlemen as much as possible.
My daughter, who's 7, has asked me if she can have snapchat. I've never mentioned it to her or even used snapchat, so she must have picked it up at school. I don't even know if she knows what Facebook is.
I suppose I'm a "young person". I prefer Snapchat because you can be yourself. It's private by default. There's no pressure to post amazing things. I often just post almost-spam crap that my friends and I find amusing - like doodles, bad selfies, a picture of a cool carpet. It's easier to avoid showing off - which I really don't want to seem like I am. The filters and drawing features make it easy to add info to a picture (location, temperature, pointing out things, etc).
I avoid Facebook for many reasons. You have to be careful about who your posts are seen by. It's public by default. I have colleagues, family, and people I've met just once or twice on there. Any posts I make need to be inoffensive and anodyne. Scrolling down a Facebook feed fills me with FOMO, jealousy, rage, or other negative emotions. It's obvious they don't actually want to improve the core product. I feel used.
If Facebook has an Achilles heel, it may well be privacy. Just as Security was first sign that the tide was turning against MS, so might privacy become for FB.