I am tired of pasting dozens of links at people, so I've loaded a bunch of the papers into Paperpile and exported a bibliography. You can find a collection of 34 papers on social media's effects on teenagers (and sometimes adults) and alternate hypotheses here:
paperpile.com/shared/smMqS...
Hall JA Ten myths about the effect of social media use on well-being J. Med. Internet Res. • Dissing AS et al. Smartphone interactions and mental well-being in young adults: A longitudinal study based...