In the last decade, research has provided a series of insights into how and why the use of social networking sites (SNSs) can be socially and psychologically beneficial for individuals. The present research extends this evidence by focusing on the concept of social closeness as a feeling experienced when using SNSs. In a laboratory setting, participants (N=60) spent 10 minutes on Facebook, and then reported their experiences during this session. Analyses of participants' usage behavior and their experiences revealed that the more time users spent interacting with other users (e.g., commenting on updates), the closer they felt to other people. Interacting with others also predicted users' positive emotional states after Facebook use; this effect may be explained by the perception of social closeness. This study is one of the first to employ momentary measures, offering a further theoretical link between active SNS use and well-being.