Harmful and illegal content on social media remains pervasive, posing significant challenges for content moderation and user safety. A key element of platforms’ moderation systems is user-driven reporting to flag such content, yet little is known about who actively reports it, their motivations, and how they differ from the general population. This study addresses two central questions: Who acts against harmful and illegal content, and to what extent have nudges promoting counter-speech and civic duty an effect on reporting behavior? We conducted two complementary studies. Study one analyzes unique survey data from two populations in Germany: a novel dataset on confirmed reporters and a representative sample. This study explores demographic, political, attitudinal, and behavioral differences between these groups. Building on these insights, study two examines nudging interventions aimed at encouraging broader reporting participation. Conducted in Germany and the United States, this representative, preregistered survey experiment tests the effectiveness of nudges emphasizing civic duty as a motivator to mitigate imminent risks posed by illegal content, as well as the potential of counter-speech as an alternative approach. Respondents are randomly assigned to control or treatment conditions, with measures of political and social attitudes included to explore their influence on behavior. By integrating unique survey data and cross-national experimental approaches, this research provides novel insights into the motivations and behaviors of online content reporters.