Aim/Purpose: This study aims to uncover how Social Network Sites (SNSs) active users who are eager to be knowledgeable about a specific domain develop a professional identity, what practices they use, and how do SNSs afford professional identity development. Background: Some researchers have shown that SNSs play a central role in personal development, but there is a lack of studies tracing the actual role of SNSs affordances in professional identity development. Methodology: Seven participants were followed during a whole year; we examined their professional identity development based on data collected from interviews, cued retrospective reports, and online activities. Contribution: The study shows that SNSs create a new context for professional identity development, a context whose new characteristics bring specific actors to a spectacular development in their professional identity. Based on the findings we suggest a new framework of professional identity development with SNSs. Findings: We identified a wide range of activities and changes in the perceived professional identity. We found that there are four phases of SNS's professional identity development. The study also uncovers the three aspects of identity development: self-presentation, around-the-clock sociality, and interaction with information. The model of professional development through intensive use of SNSs is validated by our reports on the actual behaviors afforded by SNSs. Recommendations for Practitioners: The conceptual framework displayed in the article can help educational institutions to implement SNSs in order to enhance professional identity development. Guidance will allow students to handle self-presentation, sociality, and information management. By doing so, the guides will help achieving meaningful SNS activities and encouraging students to be involved in their fields of interest, thereby enhancing their professional identity. Future Research: Future studies may examine the implementation of SNSs for the exploration process leading to identity development in various educational institutions. A few years longitudinal study may examine the lifelong professional identity development in varied SNSs. Moreover, in the COVID-19 world crisis when life is in digital spaces more than ever, it will be interesting to study the role of SNSs of professional identity development in the population that lost their jobs.