Objective: Examine 1) whether observed social reinforcements (i.e., "likes") received by peers' alcohol-related social media posts are related to first-year college students' perceptions of peer approval for risky drinking behaviors; and 2) whether associations are moderated by students' alcohol use status. Participants: First-year university students (N = 296) completed an online survey in September, 2014. Method: Participants reported their own alcohol use, friends' alcohol use, perceptions of the typical student's approval for risky drinking, and ranked 10 types of social media posts in terms of the relative numbers of "likes" received when posted by peers. Results: Observed social reinforcement (i.e., "likes") for peers' alcohol-related posts predicted perceptions of peer approval for risky drinking behaviors among non-drinking students, but not drinking students. Conclusions: For first-year college students who have not yet initiated drinking, observing peers' alcohol-related posts to receive abundant "likes" may increase perceptions of peer approval for risky drinking.