Self-disclosure taking place in computer-mediated communication (CMC) is generally associated with enhanced well-being because it evokes a greater sense of connectedness. It has been established that the magnitude of the benefits reaped from online self-disclosure is conditional on social anxiety (under the lens of the poor-get-richer vs. rich-get-richer hypotheses) or audience size. What remains to be understood is whether those with low (compared to high) social anxiety experience greater social connectedness and subjective well-being in dyadic and/or masspersonal CMC. A sample of 411 Canadian undergraduate students (aged 17–21 years old) self-reported their anxiety in social situations, online self-disclosure in dyadic and masspersonal communication, current feelings of social connectedness, and subjective well-being. Model 7 of the PROCESS macro for SPSS was used to test the indirect effect of online self-disclosure on subjective well-being through feelings of social connectedness, conditioned on values of social anxiety. The model was run separately for dyadic and masspersonal CMC. Online self-disclosure was associated with positive outcomes only for those with high social anxiety. In both contexts, online self-disclosure was associated with enhanced social connectedness and in turn more positive subjective well-being. In contrast, for those with low social anxiety, increases in self-disclosure in masspersonal CMC was associated with decreases in social connectedness and poorer well-being. The indirect effect was not significant for dyadic CMC. Overall, the findings contribute to a more informed understanding of online self-disclosure as a double-edged sword. Theoretical implications for the poor-get-richer and rich-get-richer perspectives are discussed.