Background: In recent years, there has been a growing concern regarding social media driving the decline of mental health, especially among adolescents. However, scientific consensus remains mixed, with many studies reporting only small or inconsistent associations. Aims: This paper aims to present the latest and most influential findings in the field of social media, with a focus on understanding the impact it has on adolescents’ mental health by looking at clinical versus non-clinical populations. Method: We conducted a comprehensive search through Scopus, looking for scientific articles and reviews published from January 2020 to March 2026 that include social media and adolescents with mental health conditions. We examined social media use patterns, affordances, mechanisms of impact, and clinical versus non-clinical populations. Results: There is limited literature comparing clinical versus non-clinical adolescent populations. Adolescents with mental health disorders spend more time online, teens with internalizing conditions report being more prone to social comparison and more sensitive to digital feedback, while those with externalizing conditions report a lack of control over how much time they spend on social media. Screen time alone is not sufficient to determine the impact on mental health. Among the features that might be associated with mental health problems are sharing personal content and scrolling through others’ posts. Conclusions: The impact of social media could be shaped by pre-existing vulnerabilities. There is a need for longitudinal study designs to test temporal associations and more research to cover the gap on clinical populations to develop better policies and interventions.