The popularity of social networking sites (SNSs) has increased rapidly. SNSs are a key part of daily life for many people around the world. The use of SNSs is already a global phenomenon. Drawing on social capital theory, this research empirically explored how structural capital (social network ties), relational capital (trust in SNSs, trust in members of SNSs, social identification, and social norms), and cognitive capital (shared language and shared goals) influence stickiness, which in turn affects addiction. This study introduced key moderators, privacy concerns and perceived security, to the relationship between stickiness and addiction. The authors empirically evaluated the proposed model by using survey data collected from SNS users. Structural equation modeling was applied to test the model. This study can provide a deeper understanding of SNS users' addiction behavior by focusing on social capital theory, privacy concerns, and perceived security and therefore contribute to both research and practice.