Social media, which enables instant access to resources and assistance while promoting collaboration among educators through the formation of various communities of practice (CoPs), is increasingly being used to facilitate lifelong learning and professional development for teachers. However, not all social media–based CoPs yield satisfactory outcomes for teachers, and there is a lack of comparison of the disparities between effective and ineffective communities. This study conducted a mixed survey (questionnaire and interview) among primary and secondary school teachers in mainland China to explore community characteristics that contribute to teachers’ effective learning and training. The findings indicate that significant distinctions were perceived in the characteristics of domain, community, and practice between the highly satisfying CoPs and those that elicited lower satisfaction levels. Variables such as social connection, thematic focus, interaction patterns, offline support, and leadership were found to play a crucial role in determining the effectiveness of social media–based CoPs. Factors like region, gender, or member quantity were less important.