Purpose: Social media use has increased rapidly during the past decade, raising concerns about adolescents who display problematic social media use (PSMU), as indicated by addiction-like symptoms (e.g., preoccupation, tolerance). We aimed to assess the extent to which an individual resource (health literacy), and social resources (friend support and family support), moderated the association between a range of individual characteristics (gender, age, family affluence, and depressive feelings) and PSMU; also the association between PSMU and health outcomes (selfrated health, life satisfaction, and sleep difficulties), both cross-nationally and nationally. Methods: Our sample included 22,226 adolescents from six European countries. We used data from the Health Behaviour in School-aged Children cross-sectional survey (2017/2018). Randomeffects models and moderator analyses were applied. Results: Six moderations were found, with the resources moderating the association between individual characteristics and PSMU. One moderation emerged cross-nationally, namely that a higher level of family support was associated with a lower likelihood of PSMU, especially among adolescents who did not have frequent depressive feelings. In addition, five national moderations were identified. For example, a higher level of health literacy was associated with a lower likelihood of PSMU among Finnish girls. The resources were also found to moderate the association between PSMU and health outcomes, with two moderations emerging cross-nationally. For instance, a higher level of family support was related to higher self-rated health, especially among problematic users. In addition, nine national moderations were identified; these included a higher level of health literacy being associated with having less sleep difficulties, especially among problematic users in Germany. Discussion: In adolescence, health literacy, family support, and friend support have the potential to moderate the association between individual characteristics and PSMU, and between PSMU and health outcomes, cross-nationally and nationally. We recommend the use of universal and targeted interventions to promote individual and social resources to counteract PSMU.