As the use of social network sites (SNS) proliferates, more people than ever are becoming connected to one another. Nonetheless, we have little knowledge about how certain characteristics of SNS fulfill their users' need for social connection and enhance this connectivity. Building on uses and gratification theory, this study of Twitter users posits that users are drawn to SNS to fulfill their social connection needs and that the sense of social presence SNS engender plays a significant role in fulfilling these needs. We argue that this sense of social presence is formed by immediacy-related characteristics (represented as immediate feedback) and intimacy-related characteristics (represented as feelings of privacy and responsiveness) of SNS in Twitter. We further investigate how those characteristics operate differently on mobile and non-mobile users. To test our hypotheses, we conducted a cross-sectional survey of 798 Twitter users and analyzed their responses using a structural equation model. The results support our research model. Furthermore, analysis of the responses of 367 primarily mobile users and 161 primarily desktop users indicates that the linkage between immediacy-related characteristics and social presence is stronger and the linkage between intimacy-related characteristics and social presence is weaker among mobile users than desktop users of Twitter.