Objective: Previous research has indicated the existence of a relationship between social media use and loneliness, but the nature of this relationship is not yet established. Thus, the purpose of this systematic review was to examine social media use in terms of active and passive use, as well as time spent on social media in relation to subjective loneliness among adolescents and young adults, 10-24 years, in non-clinical and clinical populations. Method: Literature searches were conducted through the databases Psychinfo and Medline. Duplicates were discarded before the articles were reviewed based on inclusion- and exclusion criteria, and went through quality assessment. The results were summarized through a narrative approach. Results: Nine articles were included in the final sample, with a total of 7100 participants. Three of the seven studies which examined time spent on social media found positive associations with loneliness, four of the studies found no associations, and one study found a negative association with loneliness. One of the three studies who examined passive and active social media use found a positive association with loneliness, while two of the studies did not find any associations with loneliness. All identified associations were weak or nonexistent. Discussion: Few studies were identified in working with this review, and the results were contradictory. Limitations in some of the studies, as well as the fact that approaches in the studies differed, made it even more difficult to draw any unitary conclusions from the results. Conclusion: More research in general, longitudinal and experimental studies in particular, is needed to examine the relationship between loneliness and social media among youth, especially in clinical populations.