Martin's team recruited more than 200 college students and had them fill out questionnaires to evaluate their levels of extroversion, paranoia, enjoyment of social interactions, and endorsement of strange beliefs. (For example, they were asked whether they agreed with the statement, “Some people can make me aware of them just by thinking about me.”)
Participants who showed higher levels of social anhedonia — a condition characterized by lack of pleasure from social interactions — typically had fewer Facebook friends, shared fewer photos, and communicated less frequently on the site, the researchers found.
Meanwhile, those who hid more of their Facebook activity before presenting their profiles to researchers were more likely to hold odd beliefs and show signs of perceptual aberrations, which are irregular experiences of one's senses. They also exhibited higher levels of paranoia.
This is nothing you don't already know, really. Think about the friend who you tag in a non-embarrassing photo at a bar on Saturday night, yet insists on untagging it and having your take it down. OF COURSE he's “showing signs of perceptual aberrations.” In fact, the dude is straight up paranoid. Meanwhile, the weird, anti-social guy down the hall who's dorm always smells like peanut butter and stale cheese probably doesn't ever update his Facebook profile, mostly because he doesn't care to interact with anyone, online or off.
See: Facebook and real life aren't all that different.