In practice, the operation of communities of practice in firms is not activated, and they are often discontinued or stagnant due to a lack of voluntary participation. On the other hand, while non-professional knowledge communities such as portal sites and café-type communities in which ordinary individuals participate continue to thrive, research targeting both professional and non-professional knowledge communities is difficult to find. Based on social cognitive theory, innovation diffusion theory, and social capital theory, this study extracted self-efficacy, perceived relative advantage, perceived compatibility, reciprocity, and trust, and examined their effects on knowledge-sharing activities (knowledge acquisition, knowledge provision, and knowledge utilization), as well as the effect of knowledge-sharing activities on community activation. For the moderating effect, the interaction effect of voluntary knowledge provision willingness was examined by distinguishing between professional and non-professional knowledge communities. A survey was conducted targeting portal sites, café-type communities, and corporate knowledge communities, and a total of 297 questionnaires were used for analysis. The research findings are as follows. First, in knowledge communities, self-efficacy, perceived relative advantage, and reciprocity had significant effects on knowledge acquisition, while perceived relative advantage, reciprocity, and trust had significant effects on knowledge provision. Knowledge acquisition had significant effects on both knowledge utilization and community activation; knowledge provision had a significant relationship with community activation; and knowledge utilization showed a significant relationship with community activation. Second, in analyzing the moderating effect of voluntary knowledge provision willingness by distinguishing between professional and non-professional knowledge communities, it was found that in professional knowledge communities, perceived compatibility and trust had moderating effects with voluntary knowledge provision willingness, whereas in non-professional knowledge communities, only trust had a moderating effect with voluntary knowledge provision willingness. Based on these research findings, academic and practical implications were presented, and limitations and future research directions were discussed.