Self-presentation is a major preoccupation in Facebook. Users carefully construct their online profile and assiduously edit postings on their wall in order to strategically shape their online persona. This study examines some psychological antecedents and consequences of such actions. In particular, we propose that users' self-esteem affects their sense of agency and self-monitoring tendencies, with the former leading to a fuller description of their profile and the latter contributing to more frequent customization of their wall. In turn, these behaviors are hypothesized to contribute to users' personal and social identity respectively, en route to affecting their valuation of Facebook as a virtual possession. Structural equation modeling analysis of survey data (N=221) largely supports this model and reveals that the personal identity reflected in one's Facebook account is a major predictor of the degree to which one values it as a possession. We discuss the implications of "I" vs. "Me" in self-esteem with regard to virtual possessions in social networking environments.