Tell me what you post and I'll tell you what you are.It should be noted that the frequently quoted argument that social media are used to promote unrestrained self-presentation can be refuted. Contrary to what is commonly assumed, the online behaviour corresponds quite well to the offline behaviour . If so, it may make sense to take a closer look at the relationship between personality traits and postings . For this purpose, a user's personality profile is created and then set in relation to her/his Facebook usage and the number of Likes or comments in response to the posts. A study showed that the personality profile of a participant predicted not only the topic of posts but also the number of likes and comments. The following insights could be gained:
- People scoring high on conscientiousness are organized and goal-oriented. They used Facebook to communicate and share content and - remarkably - released more status updates about their children.
- Openness is associated with the joy of new and unusual experiences. People who are strong in this personality trait created more status updates on "intellectual issues". They use Facebook more as a source of information and less to connect socially with other users.
- People with high extraversion values are sociable and outgoing. They used Facebook primarily as a means of communication and tended to post more frequently about social activities and daily life.
- Neuroticism is characterized by anxiety and insecurity. Participants with a high level of neuroticism used Facebook as a means of affirmation: They posted to get support from friends for their feelings and opinions when they felt isolated in their views.
- Narcissistic users are concerned about their self-presentation and want to impress and influence their own image with others. Similar to users with a high level of neuroticism, they used Facebook as a means of confirming and assuring others. Narcissists tended to publish more status updates that relate to their personal performance in life (diets, fitness routines). They were encouraged to do so by the fact that they received more feedback and comments on their posts than the other users reported.
- People with low self-esteem used Facebook for self-expression rather than for affirmation. If they were in a relationship, they posted more updates with their partner. The researchers interpreted this in such a way that they wanted to make the claim to their partner publicly clear.
The influence of the Dark Triad.Now Facebook and other social media are not the focus of criticism because conscientious parents post too many pictures of their children or narcissists post too many pictures from the gym, but because there is a problem with hatred and psychological violence. The cause is known as the "dark triad". The term refers to three overlapping personality traits: Machiavellianism, narcissism and psychopathy. People with a strong Machiavellian character are cynical, unprincipled and see manipulation as the key to success. Narcissists show grandiosity, claim, dominance and superiority. Both properties are closely related to psychopathy. Psychopaths show a low degree of empathy, combined with a high degree of impulsivity and the desire for thrills. The border to sadism is fluid .
Internet trolls are characterized by such personality traits . Trolls are only a minority, but they face a passive majority. Trolling others gives them the kick they are looking for and so they agree with statements like these taken from the GAIT-questionnaire (Global Assessment of Internet Trolling):
‘I have sent people to shock websites for the lulz’’,
‘‘I like to troll people in forums or the comments section of websites’’,
‘‘I enjoy griefing other players in multiplayer games’’
‘‘The more beautiful and pure a thing is, the more satisfying it is to corrupt’’
Another study  investigated which profiles trolls prefer to attack. An important result: Perceived popularity can attract attention and harassment. The individual characteristics of the dark triad predicted different behaviours towards popular and less popular Facebook profiles, associating psychopathy and narcissism with popular Facebook profiles.
Social media can make you feel lonely and enviousBut you don't have to be the victim of trolls. The mere use of social media seems to be sufficient. It was found  that the more people used Facebook the previous time, the worse they felt the next time. And the more they used Facebook for two weeks, the more their life satisfaction decreased over time. An effect that direct interaction with other people did not have. The effect was also not moderated by the size of people's Facebook networks, their perceived helpfulness, the motivation for using Facebook, gender, loneliness, self-esteem or depression. (6) These results fit well into the early research on alienation through the Internet: The more intensively people used the web, the more lonely and depressed they felt. 
The cause of the decline in life satisfaction was also identified: envy of "Facebook friends". Particularly affected are those who themselves hardly communicate in social networks, but only lurk. In some cases, envy leads to a more pronounced self-presentation in the social network, which in turn creates feelings of envy in others. Incidentally, #1-object of envy in Germany (both offline and online) is the subject of travel and leisure. 
Social media - cause or symptom?Just because people are social beings by nature, they are not automatically competent in dealing with social media. Obviously, we have to learn how to handle it responsibly. And it must be possible to hold people accountable who act irresponsibly. Here the suppliers have to do their homework. It is also possible to find a positive relationship between the intensity of the use of social media and life satisfaction, and even variables such as civic engagement and political participation . It all depends on how the individual deals with it. Anyone who exchanges information on common topics with people who mean something to him or her is better off than anyone who scrolls through posts with large audiences and only gets a click-feedback.  Other media such as television ("TV makes kids sick, stupid, violent, fat and lazy") also had a bad reputation at first, but over time they were able to develop their positive potential.
(1) Back, M. D., Stopfer, J. M., Vazire, S., Gaddis, S., Schmukle, S. C., Egloff, B., et al. (2010). Facebook profiles reflect actual personality, not self-idealization. Psychological Science, 21, 372–374. (Link)
(2) Marshall. Tara C., Lefringhausen, Katharina, Ferenczi, Nelli (2015).The Big Five, self-esteem, and narcissism as predictors of the topics people write about in Facebook status updates. Personality and Individual Differences 85, 35-40. (Link)
(4) Buckels, Erin E., Trapnell, Paul B., Paulhus, Delroy L. (2014).Trolls just want to have fun. Personality and Individual Differences 67, 97-102. (Link)
(5) Lopes, Barbara, Yu, Hui (2017). Who do you troll and Why: An investigation into the relationship between the Dark Triad Personalities and online trolling behaviours towards popular and less popular Facebook profiles. Computers in Human Behavior 77, 69-76. (Link)
(6) Kross, E., Verduyn, P., Demiralp, E., Park, J., Lee, D. S., Lin, N., Ybarra, O. (2013). Facebook use predicts declines in subjective well-being in young adults. PLoS ONE, 8(8). Article ID e69841. (Link)
(7) Kraut, Robert, Patterson, Michael, Lundmark, Vicki, Kiesler, Sara, Mukophadhyay, Tridas, Scherlis, William (1998). Internet paradox: A social technology that reduces social involvement and psychological well-being? American Psychologist, Vol 53(9), 1017-1031.(Link)
(8) Krasnova, H., Wenninger, H., Widjaja, T., & Buxmann, P. (2013). Envy on Facebook: A Hidden Threat to Users’ Life Satisfaction? Paper for the 11th International Conference on Wirtschaftsinformatik. (Link)
(9) Valenzuela, S., Park, N., Kee, K. F. (2009), Is There Social Capital in a Social Network Site?: Facebook Use and College Students' Life Satisfaction, Trust, and Participation1. Journal of Computer-Mediated Communication, 14: 875–901. (Link)
(10) Burke, M., Kraut, R. E. (2016), The Relationship Between Facebook Use and Well-Being Depends on Communication Type and Tie Strength. J Comput-Mediat Comm, 21: 265–281. (Link)