Many researchers have found that the main reason teachers participate in peer-to-peer professional development networks (PDNs) is to seek and share professional knowledge. Yet, the majority of studies about PDNs focus on how and why teachers participate in these virtual spaces rather than how teachers find and distribute knowledge. Each PDN has its own unique rules, tools, community members, and culture that shape how knowledge is created, organised, curated, and shared. Without understanding the factors that shape how and why knowledge is shared in a PDN, teachers may not be able to access the knowledge they need to grow their practice. This study was designed to examine teachers' knowledge seeking and sharing actions in the Edmodo Math Subject Community, a popular PDN. Cultural historical activity theory was used as a framework for examining the socially constructed actions of seeking and sharing knowledge in a PDN. The findings suggest that seeking and sharing knowledge is a complex, dynamically evolving process that is shaped by the technical (e.g., tools) and social (e.g., community members, rules, roles) aspects of the PDN. Implications and ideas for further research are discussed.