This paper outlines a research in progress set to study network effects in social media. The focus is on outlining the theoretical framework in which this study is embedded. The concepts of cumulative network effects and segmentive network effects are introduced to explain the processes by which social media can generate and maintain both a larger network of members (an online city) and a more personalized space within that larger network (an online neighborhood). Taking an actor network approach, it is theorized that cumulative and segmentive network effects are generated by unique assemblages of humans and objects engaged in meaningful epistemic relationships. This study contributes to theory by considering how the two network effects can be simultaneously fostered on the same platform and by taking technology into account as an active actor in online human activities.