While an increasing number of firms are adopting enterprise social media (ESMs), it is unclear whether these systems lead to greater participation. In this paper, we theorize that the workgroup feature of ESMs would enhance user participation as they allow users to see content relevant to their work. Yet, it is also true that the rigid communication structure of workgroups works against casual, personal style of communication that social media sites have, which can stifle user participation on ESMs. We formally study the impact of ESMs by contrasting the difference in user participation level of firms that use ESM with workgroups with those that do not, under a difference-in-difference framework. The analysis shows that users participate more after workgroups are introduced. To account for endogeneity concerns, we employ matching to derive a statistically comparable set of firms. Our analyses also show that managers are the main group of users who stand to benefit from the feature of workgroups. Implications of our results are discussed.