Identity theories have been used to understand exercise behaviours. Being part of an exercise group has been shown to strengthen one's exercise identity, with stronger exercise-related identities associated with greater efficacy, more positive beliefs and greater exercise engagement. Groups formed on social media platforms are a common way to connect with others, and evidence suggests that people use these forums to create/present certain identities. The current study examined how running group members use social media in relation to their exercise behaviours and whether use of these online groups impacts members' identities. Running group members (N=34, Mage=41) completed online measures of running behaviour, identity, Facebook addiction, and use of the running group's social media site. The majority of the participants (79%) posted their running behaviour on at least one social media outlet. They did so to motivate others, or because they were proud of their accomplishments. When confronted with not being able to post their running behaviour, 35% of participants reacted negatively. Regression analysis showed that after controlling for time with the group, Facebook use and use of the running group's social media site accounted for 54% (p<.001) of the variance in group identity; use of the social media site was the only significant predictor (p<.001). In a second regression predicting runner identity neither social media use variable was a significant predictor. Despite a small sample size, the findings extend previous work in identity and exercise by highlighting the importance of social media use as a factor in identity formation.