Amidst rising concerns about mental health in adolescents, the role of social media (SM), particularly highly visual platforms such as TikTok, has become a growing focus of investigation. In the extant literature, conclusive evidence is limited by the aggregate analysis of very heterogeneous SM platforms. This systematic scoping review examines the relationship between TikTok and mental health in adolescents. Additionally, it aims to highlight potential interactions between typical developmental processes and the unique aspects of TikTok, exploring their relevance to mental health within this demographic. Following PRISMA guidelines, a systematic search across PubMed, Scopus, Web of Knowledge, and PsychINFO yielded 20 studies that met the inclusion criteria, encompassing a total of 17,336 subjects from 10 countries. The retrieved studies analyzed four main topics related to TikTok use, i.e., the overall impact on adolescents’ mental health, risk of problematic use and behavioral addiction, consequences on body image and self-esteem, and possible spreading of mental illness behaviors. While TikTok offers creative opportunities for self-expression and peer connection, the literature raises concerns about its potential negative effects on teens, such as lower life satisfaction, increased risk of “contagion” of certain psychiatric symptoms, and problematic usage patterns. Significant variations in study methodologies and outcome measures were observed. In the current era of evolving SM landscapes, a comprehensive approach informed by developmentally grounded research is critically needed to further understand the interplay between SM and adolescent mental health, providing insights for health authorities and policymakers.