Moving beyond examining overall social networking site (SNS) use, this study examined the influence of three types of WeChat activities on loneliness, considering the moderating roles of age and perceived network supportiveness on WeChat. Results of a two-wave panel survey with Chinese WeChat users ( N = 1202 at Time 1, N = 740 at Time 2) revealed that frequent directed communication, content consumption, and broadcasting on WeChat did not directly influence participants’ loneliness across age cohorts over time. However, the effects of WeChat activities on loneliness were contingent upon a user’s age. Moreover, the positive role of WeChat activities in alleviating loneliness was significant only for users who perceived higher levels of network supportiveness on WeChat. For users who perceived lower levels of network supportiveness, frequent WeChat activities led to increased loneliness over time. These findings contribute to a more nuanced understanding of the implications of mobile SNS use on well-being across generations in the longitudinal context.