This study examines whether the emerging communication environment makes people perceive media as more or less biased. Do social media contribute to the perception of a hostile media environment? Or do they promote a “friendly” media phenomenon through processes of selective affiliation/exposure and/or user filtration of disagreeable content? Based on the idea of egocentric publics, that is, the emergence of socially networked publics that are key for our understanding of current communication processes and examining these questions in a politically polarized society—Colombia—results indicate that reliance on social media for news exacerbates the perceptions of media bias. These perceptions of bias in turn foster political action in both the “campaigning” and “complaining” dimensions of political engagement. Thus, egocentric publics can be sources of political mobilization, but part of their mobilizing influence works through perceptions of a biased communication environment. Implications of these findings are discussed.