Social networking sites (SNS) play a central role in shaping adolescents' identity, offering constant spaces for exposure and comparison. Empirical evidence highlights a link between intensive SNS use and narcissistic traits, particularly vulnerable narcissism, which is characterized by communicative ambivalence and a persistent need for approval. Passive SNS use, defined as browsing without active interaction, has been associated with reduced self-esteem and heightened personal insecurity. Moreover, while SNSs can foster digital connections, they may negatively affect adolescents' sense of community, understood as perceived belonging, value sharing, and active participation. This study examined the relationships among vulnerable narcissism, self-esteem, SNS use, and sense of community in adolescence. A sample of 467 Italian high school students (aged 15-22 years) completed validated self-report measures of these constructs. Results revealed a negative association between vulnerable narcissism and sense of community, with self-esteem mediating this relationship. Specifically, higher levels of vulnerable narcissism predicted lower self-esteem, which in turn was associated with reduced community connectedness. Furthermore, SNS use moderated these associations: under low SNS use, vulnerable narcissism was negatively related to both self-esteem and sense of community, whereas under high SNS use, these relationships became positive. These findings underscore the complex role of SNSs in adolescent development. While limited use may amplify tendencies toward withdrawal, more frequent engagement can provide protective feedback mechanisms that reinforce self-worth and support community integration. The results suggest that interventions should not simply discourage SNS use but rather promote conscious and balanced engagement. Programs fostering emotional awareness, critical reflection on online feedback, and authentic self-esteem development may help adolescents transform vulnerable narcissistic tendencies into opportunities for constructive community participation.