Social media isn't a cause because there is nothing you can do with it that couldn't be done before it existed. However it doesn't mean that it makes some things more or less likely.

There are numerous studies at the individual level attributing the rise of various mental health problems to social media. That's not really debatable at this point; what is more interesting are the social repercussions, looking at the effects on whole populations. This is one of the topics of the books I mention.