Annual Research Review: Adolescent social media use is not a monolith: toward the study of specific social media components and individual differences.

Social media have drastically changed the context of adolescent development. To date, the majority of research investigating the effects of these changes has measured time spent on social media, yielding inconclusive results-likely because this approach conceptualizes social media as a monolith. Social media experiences are complex and diverse, as are adolescents themselves. Emerging research has identified several specific components of social media that have varied associations with adolescent mental health, as well as individual difference factors that may alter these associations across adolescents. In this annual research review, we synthesize evidence regarding heterogeneity in social media effects related to (a) specific components of social media and (b) adolescents' individual differences regarding social media use and effects. We first focus on the specific social media components-content, features, and functions-that may be especially relevant for adolescent development. These include functions designed to foster relationships and social connections (e.g., social media feeds, 'friends'), hateful content, notifications, risky content, and algorithmically curated content, among others. Next, we provide an overview of for whom these effects may matter most. We review research on individual differences that may explain some heterogeneity in social media effects, including gender/sex, age, marginalized status, neurobiological and social sensitivities, and other preexisting vulnerabilities to mental health concerns. The nascent work in these areas suggests many specific constructs and considerations that could drive future research examining nuanced and precise questions that go beyond 'screen time'. We discuss avenues for researchers to leverage methodological advancements and address how specific social media experiences and individual differences shape developmental outcomes.