This study aims to investigate users’ subjective well-being and loyalty towards social network sites (SNSs). Despite the growing role of network externalities in SNS continuance decisions, the SNS usage literature has paid scant attention to the relationship between network externalities, SNS identification, and users’ subjective well-being. In this study, we identify four components of network externalities: perceived network size, external prestige, compatibility, and complementarity. In the research model, both network size and external prestige are hypothesized positively to affect SNS identification. Perceived compatibility and perceived complementarity are hypothesized positively to affect user satisfaction. Satisfaction and SNS identification are hypothesized positively to affect user subjective well-being and loyalty towards the SNS. Users’ subjective well-being is hypothesized positively to affect their loyalty towards the SNS. Data collected from 615 valid users of Facebook provide strong support for most of these hypotheses. The findings indicate that perceived network size negatively affects users’ SNS identifications. Other components of network externalities have positive effects on SNS identification and satisfaction, which in turn have positive effects on users’ subjective well-being and loyalty towards SNS. Implications for theory and practice and suggestions for future research are also discussed.