This narrative review examines the influence of social networks on dietary habits and physical activity, and their relationship to overweight and obesity in adolescents. The study is based on a comprehensive literature search across PubMed, Scopus, EMBASE, PsycINFO, and Web of Science databases, covering the period 2009–2022, and is complemented by a critical analysis of contemporary evidence. The included studies involved adolescents aged 12 to 19 and assessed associations among social networks, body weight, diet, and physical activity, using statistical methods based on social network analysis (SNA). No language restrictions were applied. The results demonstrated that friendship networks significantly influence adolescents’ body weight, eating behaviors, and physical activity levels. Specifically, boys exhibited similar unhealthy food consumption patterns within their networks, while girls’ networks showed similarities in sedentary activities. This review highlights that adolescents’ social networks play a relevant role in weight-related behaviors, with their influence varying based by gender. These findings underscore the need to consider such gender-specific effects when developing prevention and treatment strategies for obesity in this age group.