In this diploma thesis I explore the topic of publics on online social networking sites. I also focused on how the concept of publics affects how users behave and present themselves on online social networking sites, taking Facebook as an example. Identity management is an extensively researched area. However, less attention is paid to understanding the ways how users define their audience and how precise such a concept can actually be. In this thesis I set to understand how teenagers think and conceptualize different types of audiences they may encounter and how such imagined audience influences the way they use Facebook. Since this is a topic considerably difficult to think of let alone speak about, especially for young people, I chose projective techniques used in a focus group to overcome these obstacles. Using this method I tried to get answers on the research questions and obtain an insight as to how people imagine their audiences on online social networking sites, what are the most prominent types of users, and how it affects, in turn, their usage of Facebook. A similar type of research can be conducted also for other groups of online social networking sites users as well as for other online social networking sites. The next possible step can be a quantitative study assessing the stated..