This study explored how a group of academics in China and Europe used WeChat to build a Community of Practice online, which supported their interdisciplinary collaboration and professional development. We primary used a qualitative research design, combining with a data mining technique, and the qualitative data were mainly from multiple sources including online interaction excerpts, teachers' reflections, and interviews. The results showed that the participants were utilizing the WeChat App to build a virtual CoP for collaboration and professional learning in terms of three dimensions: mutual engagement, joint enterprise, and shared repertoire. Positive perceptions were identified in these participants on joining the different groups. Moreover, their research collaboration and knowledge in different fields were transformed positively. The participants were clustered in three groups and the results showed that their positive attitudes of engaging in the CoP could be reflected according with their tendency, perceptions, and willingness of using WeChat in the analysis. A framework for using mobile social media to transform CoPs into knowledge-building communities for academics' collaboration and learning was proposed based on the findings. Future directions are also provided.