Online health communities (OHCs) often struggle to retain active users because they endow users with both a positive and a stigmatized social identity that respectively encourages and discourages their engagement. We integrate social identity theory with the concepts of social stigma, psychological capital, and digital divide to investigate this phenomenon. We collected survey data from 221 users from one large online lymphoma community in November 2017. We find that users' positive social identity had a positive influence on how they perceived the effectiveness of OHCs and this influence was stronger for the high socio-economic status (SES) group; at the same time, a stigmatized social identity had a negative influence on perceived effectiveness of OHCs and this influence was stronger for the low SES group. Moreover, users’ perceived effectiveness of OHCs had positive influences on their participation and recommendation intentions, and the influences on participation and recommendation intentions were stronger for the high and the low SES group, respectively. Our study highlights the dual influences of valenced social identities on user engagement with OHCs through their effectiveness perceptions and interprets these influences through the lens of digital divide. The findings also offer practical insights for the effective management of OHCs. •Positive social identity increases perceived effectiveness of OHCs.•Stigmatized social identity decreases perceived effectiveness of OHCs.•Perceived effectiveness of OHCs positively impacts user engagement.•SES moderates the impacts of valanced social identities on perceived effectiveness.•SES moderates the impacts of perceived effectiveness on user engagement.