Adolescents have virtually universal access to social media. Despite ample research linking attachment to social functioning in youth, neither this empirical research nor related theory has been extended to the virtual social context. The broad aim of this study was to test an attachment-based model of social media use in adolescents in order to address a gap in the literature during this developmental stage and examine attachment and the related process of mentalizing as correlates of online behavior. Online social comparison/feedback-seeking was selected as an outcome variable due to its known negative effects on adolescents. Analyses were conducted in a sample of 68 adolescents ranging in age from 15 to 18. No evidence of a main effect of parent-child attachment on social comparison/feedback-seeking was found, but a significant mediational effect indicated that more insecure parent-child attachment is linked with hypermentalizing errors (i.e., overinterpretation of others' mental states) and that such errors explain increased social comparison/feedback-seeking. The current study confirmed previously documented relations between parent-child attachment and hypermentalization as well as research demonstrating that parent-child attachment acts on an adolescent's social world - in this case their virtual social world - through anomalous mentalization.