This scoping review examined the relationship between social media use, depression, anxiety, and suicidal behaviour among adolescents aged 13 to 19 years. The review was conducted in accordance with the PRISMA guidelines and included studies published between 2014 and 2024 across 28 literature databases. Eligible studies investigated social media use in relation to at least two of the constructs: depression, anxiety, and suicidal behaviour. An initial search identified 64 potential articles (N = 64), from which one duplicate was removed. Thirteen studies were excluded because they did not examine social media use in relation to the target constructs, and one was excluded for being an abstract, leaving 49 studies for full review. Of these, 40 studies were excluded: 14 due to an inappropriate population, 11 for focusing solely on social media without assessing psychological outcomes, and 15 for exploring fewer than two of the key constructs. Consequently, nine studies (N = 9) met the inclusion criteria and were analysed. The findings revealed a positive correlation between time spent on social media and symptoms of depression, anxiety, and suicidal behaviour among adolescents. These associations appeared to function both directly and indirectly through mediating factors such as boredom and loneliness. However, causal relationships remain unclear due to the predominance of cross-sectional designs and a lack of qualitative studies. Existing research largely draws from international data and frequently examines these constructs in isolation. Future studies should adopt longitudinal and qualitative methodologies to explore the mediating roles of boredom and loneliness and to clarify better the causal pathways linking social media use with adolescent mental health outcomes.