We conducted a nationwide field experiment in China to evaluate the direct and indirect impacts of assigning firms to public or private citizen appeals treatments when they violate pollution standards. There are three main findings. First, public appeals to the regulator through social media substantially reduce violations and pollution emissions, while private appeals cause more modest environmental improvements. Second, experimentally adding “likes” and “shares” to social media appeals increases regulatory effort, suggesting visibility as an important mechanism. Third, treatment pollution reductions are not offset by control firm increases, based on randomly varying the proportion of treatment firms at the prefecture-level.