Despite a rich body of research on face-work, how it is performed in online edu-social groups remains under-explored. Drawing on posts and comments of Facebook groups created for courses at a university in Hong Kong, together with interviews with students, tutors, and the lecturer, this article examines how code-switching is deployed as a powerful discursive resource in the performance of face-work. Notwithstanding English being the medium of instruction of the courses, code-switching is noticeable. Focusing on these participants' practices, our analysis discovers that code-switching serves primarily to signal the breakdown of the expectedly formal academic participation frame and the switch to an informal frame. Multiple layers of action frames are collaboratively and constantly designed and redesigned in these ‘social network-educational spaces’ (Chau and Lee, 2017), where the formal-informal, public-private, and academic-social boundaries become indistinct. Closer analysis within and across the spaces further reveals that norms of appropriateness of code-switching to achieve informality and solidarity may vary depending on a combination of individual, contextual, and temporal factors. In addition to contributing to existing literature on code-switching and face-work on Facebook, the article offers practical implications for understanding the increasingly informalized discourses in institutional contexts.