Web-based media often present multiple sources of influence, such as mass media and peers, within one interface. When individuals identify with peers who are visually anonymous and with whom they do not directly interact, they should be susceptible to social influence from that group. This study examined the interplay among antimarijuana public service announcement (PSA) videos in a YouTube environment and adjacent message postings from other viewers about those videos. Results show that supportive or derisive comments affected PSA evaluations but not marijuana attitudes, whereas the interaction effect of identification and comment valence affected both PSA evaluations and marijuana attitudes. Other factors previously related to PSA evaluation such as message strength and perceivers' sensation-seeking did not interact with hypothesized factors.