Facebook groups (FGs) have been widely used by teachers/educators. However, the type of educational FGs they value most, and the reasons for their choices, are less clear. This paper examines the perspectives of 440 participants (86% mathematics teachers and 14% mathematics teacher educators) on their educational FGs. It identifies the types of FGs they value most, the reasons for their choices, and aspects they dislike. Data collected through an online survey suggests that FGs are used for professional engagement across Indonesia. Support for FGs included the perceived benefits of sharing information/resources about mathematics (as well as education in general), networking and communication with others, opportunities for teacher professional development sessions and announcements about/access to up-to-date information. However, limitations with the platform included occasional irrelevant posts/comments, unexpected member behaviour and the lack of responsiveness from FGs administrators. Commonly, most participants saw value in discipline-specific (i.e. mathematics) engagement, leading to professional learning/support. This study stimulated further discussion on ways to maximise benefits whilst simultaneously overcoming the identified challenges of these participant-driven online communities.