To date, research on social network sites (SNSs) has primarily focused on Facebook. Professionally oriented social network sites (P-SNSs), such as LinkedIn, have been under-researched in the information systems discipline. Additionally, little is known about the effects of important elements of SNSs (such as one’s profile) on social capital formation. As such, the main objective of this research is to propose and validate a model that explains the process by which individuals develop and accrue social capital through P-SNS use. This model draws upon social capital theory and social network analysis and is validated through a survey of 377 LinkedIn users. Our results find that (1) P-SNS users’ actions (perceived profile disclosure, active participation, and passive consumption) have significant positive effects on perceived social connectedness; (2) perceived social connectedness on P-SNSs has a significant positive effect on perceived networking value on these sites; (3) perceived profile disclosure and passive consumption have significant positive effects on network size; (4) active participation does not have any effect on network size, and (5) network size does not have a significant effect on perceived networking value. Overall, this investigation advances our understanding of how social capital is formed in P-SNSs. Additionally, this is the first study in the P-SNS context that investigates the role of the user profile in the social capital formation process, along with user actions of active participation and passive consumption. From a practical perspective, this study has implications for different audiences, such as job seekers, recruiters, and P-SNS providers, assisting them in playing a more effective role in the social capital formation process on P-SNSs.