Online health communities (OHCs) have now become a valuable platform for people to seek health-related information. Knowledge sharing and community promotion in the OHCs are critical to sustain their continuous use and improve their engagement. This study aims to investigate factors influencing knowledge sharing and community promotion in the OHC in the perspectives of social support, commitment-trust, and trust transfer theory. A questionnaire survey is employed as a collection data technique. The study results reveal that informational support influences trust transfer, trust towards community and members of the community. In addition, emotional support has a positive impact on community commitment and trust in community members but not in the community itself. Further, community commitment is positively related to both knowledge sharing and community promotion. While trust towards the community is only positively related to community promotion, trust towards members of the community does not have a positive influence on both knowledge sharing and community promotion. This study contributes to the understanding of the relationships among social support, community commitment, and trust transfer towards knowledge sharing and community promotion in the OHC. The findings of the study provide a research model that could be implemented in other contexts that share similar technology landscape.