[outofcuriosity]

There've been other studies to this effect, though, and not just for adolescents. Papers often attribute the effects to a combination of lifestyle comparison, echo chambers, and emotional contagion. Check this one out: http://www.pnas.org/content/111/24/8788.full.pd

Now imagine your entire friend network is nonstop angst. I'd go mad, too.

It could be a just-so story, but I think overuse of SNSs allows our social skills to atrophy. The brain repurposes structures that go underused, and the structures that maintain one's face-to-face social functioning are no different.

Maintaining relationships in realspace is different than maintaining them in the async-y & memetic environment of cyberspace. Of course there is granularity--one can have a healthy analog&digital relationship, but if a SNS connection is a part of an individual's requirement for a friendship, then there is probably some deficit the individual is unaware of.

I'd also argue that this is symptomatic of the growing pains heavy internet users experience in their adolescence-to-young-adult stage. The group self-selects for introverts who have a preexisting difficulty with social interaction. However, we all require some social interaction (analog or digital), to greater and lesser extents, and so it perpetuates.

Books and art end up being a better outlet, but in my experience that's a discovery which people can only make for themselves.