The present study seeks to identify the behavioral antecedents to individuals' participation as protégé in a social mentoring network (SMN). It draws on social psychology and vocational literature and applies the Theory of Planned Behavior (TPB) to understand and predict the specific behavioral context. A SMN was operationally defined as a special case of informal mentoring coupled with a social networking platform. Two additional variables--similarity and self-disclosure--were incorporated into the standard TPB model to improve its predictive power. A total of 376 respondents completed their first- and second wave questionnaires in a 2-week-longitudinal survey design. Two hierarchical multiple regressions were performed to determine the unique contributions made by the extended TPB model to the variance in behavioral intention and behavior. The results indicate that intention was demonstrated as a single significant variable in determining the behavior. Furthermore, intention was significantly influenced by respondents' attitudinal and normative beliefs toward the behavior, weighted by their internal mechanism that establishes the importance of necessary preconditions for the development of successful mentoring relationship. These preconditions include protégés' need for similarity with their mentor as well as willingness to self-disclose themselves to the SMN.