Contact-tracing apps have been identified as a promising technology to curb the spread of COVID-19. To be effective, a sufficient number of individuals need to install the app and disclose information like COVID-19 infection to such an app. Yet, usage data demonstrate that a large number of app users does not disclose COVID-19 infection to the app. Hence, in two studies (overall N = 1522), we investigate factors related to individuals’ willingness to actively disclose information to such an app. In a preregistered online experiment conducted two months before the app launch onto the German market, we find that disclosure willingness increases when the app’s prosocial benefit or a social-life-enabling benefit is emphasized (vs. no benefit emphasized). In a subsequent, quota-representative survey study conducted two months after the app launch onto the German market, we adapted and extended the Technology Acceptance Model 2 (TAM2) to the context of prosocial information sharing in tracing apps. We find that the perceived prosocial benefit of the app, trust in public institutions, and fear of COVID-19 are the relevant predictors. Moreover, we demonstrate that the relation between perceived prosocial benefit and disclosure willingness is moderated by perceived ease of use. Results are discussed with regard to effective implementation and communication strategies for tracing apps, and the general role of prosocial concerns for technology usage to address major societal challenges.