Though empirically some research suggests the linkage of better communication effect with active users' presence, no existing clues are found on the user activeness at the micro level to contribute to the virtual community's aggregate-level health and vitality. This paper models the interpersonal communication process via a multi-agent, self-reasoning model. It considers each agent’s information value and conformity value, two key constructs adopted in this paper. This paper adopts simulated experiments to identify active users based on individuals’ behavioural characteristics, screen out typical users of different activeness levels, and reveal causalities among the outcomes. The findings show that users' activeness determines the information vitality and influence of information dissemination and substantially impacts the dynamics of user-groups. The author concludes with a discussion of the theoretical and methodological contributions and pinpoints these findings for marketers to improve online customer relationship management.