Social media has become a central context of adolescent development, raising concerns about its effects on body image and self-esteem. This systematic review, conducted in accordance with PRISMA 2020, synthesized empirical studies examining social media use, body image, and self-esteem among adolescents aged 10–19 years. A Scopus search identified 56 records, of which six studies (N = 2,645) met the inclusion criteria. Most studies were cross-sectional and involved girls only. Appearance-focused social media use and online comparisons with peers were generally associated with more negative body image, with social comparison and self-sexualization emerging as the mechanisms tested most directly. Evidence on self-esteem was limited and less direct: self-esteem was treated variously as an outcome, mediator, or control variable, and no study tested whether body image mediates the link between social media use and self-esteem. Longitudinal and experimental research with more diverse samples is needed, and school-based programs that combine media literacy education with activities strengthening self-esteem and self-compassion are recommended.