Social networking sites (SNSs) allow users to connect with each other by overcoming geographical and temporal boundaries and thus empower people to search for social support from online. Social support has been considered a key social value that online users can obtain from social networking sites. Research has shown that social support may reduce stress and promote well-being among diverse populations. Despite its significance to society, the online social support function of SNSs has been surprisingly under-investigated. Some fundamental questions—such as (1) What are the dimensions of online social support on SNSs? and (2) How does online social support influence other factors on SNSs?—have not been answered. This study is one of the first to attempt to answer those questions. Specifically, this study aims to first identify the definitional dimensions of online social support on SNSs through an extensive review of the literature. Second, this study uses these dimensions to model online social support and test its effects on other SNS factors: commitment and continuance intention. Eventually, the results support all proposed hypotheses. The theoretical contributions and managerial implications of this study are discussed at the end.