While I don't doubt that social media can drive some of these mental health issues, I think most teenagers are simply stressed from the constant work that's necessary for the college admissions process. I'm 24, so I would have been a teenager in 2012, but I didn't have a smartphone until I was 16 or so. My high school experience consisted almost entirely of school, studying, and running (my primary extracurricular).…
We need something like Rumspringa[1], a period in life when I young person is given a bit of slack, and is expected to eventually voluntarily take upon themselves the duties and responsibilities of an adult, or leave the community.
I can't find it now[2], but I remember either Joseph Campbell, or some other such person in a TV interview describing how in earlier societies, the children once of sufficient age would be set outside of society, and allowed to sleep in the ashes around the camp fires, until they resolved to join society as an adult, with all the privileges and responsibilities.
[1] https://en.wikipedia.org/wiki/Rumspringa
[2] google really does suck these days, doesn't it?