Compared to individual differences in antisocial and prosocial online behavior, less is known about the motivation to behave antisocially or prosocially online. In this exploratory study (N = 239), we examined the Dark Triad (narcissism, Machiavellianism, psychopathy) and empathy (cognitive and affective) as predictors of antisocial and prosocial social media motivations. Women (but not men) with high psychopathy were more motivated to use social media antisocially. Men and women with high narcissism were more motivated to use social media antisocially and prosocially. Lastly, for women (but not men), higher affective empathy and lower cognitive empathy predicted higher prosocial motivations. These results provide valuable information about the nexus between personality and online behavior and are consistent with a Uses and Gratifications approach. Findings offer an important initial contribution to understanding individual differences in the motivation to behave antisocially and prosocially online.