The communities of practice created via Facebook groups (CoPiF) have significant potential as a new mechanism in the process of the professional development of teachers when the frequency of use of Facebook and its simplicity are considered. In this study, the author analyses the content shared in a Facebook group with over 13,000 members created by several high school mathematics teachers working at different schools in Turkey in 2009. Semi-structured interviews were employed with the participating 14 teachers and the author used netnography, which is a qualitative research paradigm. The paper concluded by offering a Facebook group model for the professional development of teachers, and the positive aspects of the mechanism were explicated.