Previous research has shown that mass media stimulate the development of an objectified self-concept. However, we know little about the role social networking sites (SNS) play in these relationships. The current longitudinal study (N = 1,041) aimed to fill this gap by studying adolescents’ frequency of SNS use in general and their use of SNS to monitor attractive peers in particular. The results showed that the use of sexualizing mass media was associated with considering the appearance ideals promoted in mass media as one’s own standards to pursue. This internalization of appearance ideals, in turn, was related to the tendency to monitor attractive peers on SNS. Both the use of SNS to monitor attractive peers and the use of sexualizing mass media stimulated self-objectification and body surveillance over time. The frequency of SNS use played a limited role in the relationship between mass media and an objectified self-concept.