The goal of this research was to examine how Israeli chemistry teachers at high school level use Facebook groups to facilitate learning. Two perspectives were used: Teachers' TPACK (Technological Pedagogical Content Knowledge) and the self-efficacy beliefs of chemistry teachers for using CLFG (chemistry learning Facebook groups). Three different case studies were chosen and qualitative and quantitative research tools were used to learn about the teachers' self-efficacy beliefs and knowledge. More specifically, a validated questionnaire for measuring teachers' self-efficacy beliefs for using Facebook and for integrating Facebook into teaching was developed. We show that the initial beliefs (not based on a real acquaintance of Facebook) were replaced by more realistic efficacy-beliefs after the teachers started to work with the CLFG and that the technological support provided to each teacher, together with their mastery experience, supported the development of strong self-efficacy beliefs regarding the use of CLFG. Teachers' TPACK was investigated by analyzing their interviews and the interactions in their CLFG. We found that the notion regarding what constitutes learning in the CLFG had not changed during the experiment but rather, the teachers knew better how they can facilitate this leaning. In addition they better integrated links to videos and visualizations that supported understanding abstract chemistry concepts. Interestingly, the intervention that was conducted did not influence teachers' perceptions of learning; however, it was found to serve as an additional tool for supporting their self-efficacy beliefs by providing vicarious experience for the teachers. We therefore recommend performing a longer intervention in the future.