I'd like to see studies of how social media affects different personalities types. My intuition is that the negative effect can manifest in different ways. For example a person that has social anxiety in real life, let's say because is unconsciously worried about how to behave socially, maybe because the fear of rejection or being bullied by the group. This person would post probably close to zero, and avoid public comments, while being very anxious while waiting for a private response. I think the effect in this case, is that the person becomes even more isolated and even less social. Because these people can manage still in small groups of 4 to 5 people but I think on average we have 300 facebook "friends", that might not be manageable. And the extroverts would engage reactively only to other extroverts, causing other type of harms. That's my intuition from my direct observations.