This study examines three efficacy beliefs— political self-efficacy, political collective efficacy, and knowledge sharing efficacy—as antecedents of social media use and civic engagement. Employing more than one thousand samples in Singapore, we empirically test (a) a conceptual framework that can provide an understanding of the relationship between the three types of efficacy and civic engagement and (b) the underlying mechanism through which the three types of efficacy beliefs affect civic engagement via social media. The findings suggest that knowledge sharing efficacy was found to play an important role in mediating the relationships between social media and political self-efficacy, political collective efficacy, respectively, which, in turn, influences the social media se.