This systematic review aims to explore social media integration in K-12 foreign language (FL) classrooms in the past decade and discusses the unique challenges of adopting social media in K-12 FL teaching. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and selection criteria, 12 studies between 2010 and 2019 were selected. Adopting a grounded analytical method, this review provides a synthesis of the affordances and challenges of social media integration in K-12 FL education. Based on the data analysis, an effective approach to integrating social media in K-12 FL education is proposed, to connect formal and informal learning environments. This review concludes with suggestions and directions for future research on the integration of social media in K-12 FL classrooms.