The mental health of urban empty-nesters has become one of the most serious challenges in the wave of ageing. In the Internet era, in order to solve the dual dilemmas of physical “empty nest” and psychological “empty heart” of urban empty nesters, we need to call for the joint care of family, friends and society, while social media support is essential as well. The study focuses on the specific online social activities of this special group of urban empty nesters. It outlines the pathways through which WeChat community participation affects loneliness. These pathways involve different sources of social support. The study further explores the underlying reasons for the differences in the role of different sources of social support. It finds that friend support has a significant mediating effect between WeChat community participation and loneliness among urban empty nesters, while family support and other support have no signfiicant effect. This is a result of the interplay between multiple factors, including WeChat community attributes, physical space segregation, public opinion orientation, and individual choices. However, a single source of social support cannot hide the reality of weak emotional support and the lack of social security for the empty nesters. Therefore, a social support system should be established in the future to effectively link online and offline support and promote a balanced and diversified approach to social support.