This study examined the physical activity and motivational effects of young adults posting physical activity posts to a social networking site. It used a repeated-measures, between-group design. Fifty-eight young adults from an introductory fitness course chose to participate in this study. Participants were divided into two groups: (a) posting physical activities to social networking sites and (b) not posting physical activities to social networking sites. Participants' physical activity and motivation were tracked throughout the intervention. The social networking group was less physically active at the beginning of the intervention but did not differ significantly from the control group at the end of the intervention. A t test revealed a significant increase in physical activity from baseline for the social networking group (p = 0.001) but not for the non-social networking group (p = 0.44). There were no significant differences relative to motivational indices between the two groups, although extrinsic regulation (p = 0.06) and amotivation (p = 0.06) displayed marginal significance. Social networking has become a part of life. This platform may hold promise for increasing physical activity levels among young adults. More research is needed on how social media may influence various motivational subconstructs.