Social networking sites (SNSs) have enabled people to voice their concerns by making their voices heard and hence initiate social change. Constructive voice behavior concerning societal matters, mediated by SNSs, is a much under-explored area and requires investigation. Primarily, voice literature has mainly discussed voice behavior within organizations focused on employees. However, individuals, as members of society, are using social media websites to voice about social change in the form of condemning harmful practices in society and/or promoting social good. Drawing from the self-consistency theory, this study explores the role of an individual's moral identity as an antecedent of constructive voice behavior on SNSs. Hierarchical multiple regression analysis results of 226 SNSs users, provide support to the self-consistency theory-based moderated-mediation model in which the positive relationships, between individual's moral identity and the promotive-prohibitive voice on SNSs, were mediated by the felt responsibility for constructive change (FOCC). Further, proactive personality moderates the positive mediation effect of FOCC between moral identity and prohibitive voice but not for promotive voice, such that the mediation effect would be stronger for individuals with a high-proactive personality than those of with a low-proactive personality. This study contributes to both voice and social media research in a number of ways.