This study investigated K12 teachers' Facebook usage habits, intensity, self-disclosure, privacy settings and activities. A multi-method design was employed by collecting quantitative data from 616 teachers with a Facebook account using an online questionnaire and qualitative data from 32 teachers using online open-ended questions. The results of the study showed that Facebook seems to be part of teachers' daily routines. Moreover, they revealed that teachers were less likely to share sensitive and potentially stigmatising personal information on Facebook. Teachers were also found to set most of their Facebook privacy settings as "Friends" by taking intimacy, unwanted contacts and potential threats into consideration. Furthermore, the findings indicated that teachers felt themselves less comfortable when parents and students viewed their Facebook profiles. In addition to social engagement, teachers pointed out several ways in which Facebook was used to support educational and professional development practices. Implications, limitations and directions to further studies are discussed.