Body image refers to how individuals experience and perceive their bodies and can be affected by many factors, including peers and family members. Adolescence is a time when body image concerns are emphasized due to the bodily changes of puberty as well as increased internalization of cultural ideals and pressure to adhere to those ideals. Appearance-related teasing is one particular sociocultural factor that is gaining attention in the research field due to the emphasis placed on appearance during adolescence. The current study examined how appearance-related teasing by peers, parents, and siblings affected young adolescents' body image both directly and indirectly via social comparison. Further, because body image is a multidimensional construct and can include body dissatisfaction and drive for muscularity, the present study examined both of these constructs separately. I collected self-report questionnaires from 73 adolescent girls and 67 boys in middle school. I used Pearson correlations, linear regression, and mediation analyses to examine these hypotheses. First, I hypothesized that adolescents who were teased about their appearance by at least one of their parents would also have siblings who teased them. I found significant correlations between both fathers' and mothers' teasing and siblings' teasing, suggesting that parents are modeling teasing behaviors to their children. Second, I hypothesized that appearance-related teasing by fathers, mothers, peers, and siblings would each be associated with body dissatisfaction for girls and drive for muscularity for boys. My findings indicated that mothers', fathers', peers', and siblings' teasing predicted girls' body dissatisfaction and that mothers' and fathers' teasing predicted boys' drive for muscularity. Therefore, appearance-related teasing appears to be detrimental behavior that negatively influences adolescents' body image. Third, I hypothesized that appearance-related social comparison would mediate the relationship between appearance-related teasing from all sources and body dissatisfaction among girls and drive for muscularity among boys. Appearance-related social comparison fully mediated the relationship between fathers' teasing and girls' body dissatisfaction and the relationship between mothers' teasing and boys drive for muscularity. My findings suggest that boys and girls who were teased about their appearance were more likely to engage in social comparison, which negatively impacted their body image. Therapists need to be aware of the role family members' and peers' appearance-related teasing play in the development of adolescents' body image in order to address the occurrence and negative effects of teasing. In addition, researchers will need to conduct future studies further investigating appearance-related teasing by family members and peers and design intervention and prevention programs to address teasing and social comparison among the family and peer contexts.