This study compares the use of personal and professional social networking sites by young adults for social capital enhancing activities. The research is based on a survey of college-age adults (n=292) who were asked about their use of two social networking sites of contrasting architectures: the more interactive, social/personal\-oriented site Facebook, and the relatively less interactive, professional/business-oriented site LinkedIn. Data were analyzed to determine the relationships among demographic and technology experience factors, and respondents’ use of these sites for social capital enhancing activities. Findings suggest that increasing age and number of SNS profiles are positively related, while gender is not related significantly with social capital enhancing activities on Facebook and LinkedIn. Higher income levels were significantly and positively related with Facebook use but not with LinkedIn use. Surprisingly, the more social-oriented Facebook was used in more social capital enhancing ways than the more professional-oriented LinkedIn, suggesting that for college-age students, socially-oriented sites such as Facebook serve as a platform for the interactions which form a foundation of social connections on which more professional, social capital enhancing activities are based.