While social media is widely used by youth around the world, research is only beginning to document how transnational students employ these technologies. This study investigated how English-learning adolescents in the United States use social media to engage in social, academic, and identity work. Data were collected during a four-day social media unit in a high school English as a Second Language class of mostly recently arrived East African youth. Data sources included Facebook posts, video recordings of class interactions, student presentations, and interviews. These data were analyzed through post-structuralist identity frames (e.g., Norton, 2010) and the social semiotic construct of modality (van Leeuwen, 2005). Analyses indicated that through the process of building social presence (SP), learners asserted identities, which were affirmed by classmates, and legitimated their contributions. This legitimation resulted in rich, interactive learning experiences in the group. This finding has implications for using social media in classes with transnational newcomers.