While weblog is unquestionably a publication tool that provides individuals with original formats for recounting their personal identities, it is also a communication tool that offers diverse and original ways of putting people into contact. In this paper, blogs are considered as a relational technique enabling individuals to form relationships around the way they produce their social identity. A typology of four forms of communication, between posts and comments on blogs, is proposed in order to take into account the effects of the blog's public on its content. These four types are described using different kind of indicators, combining qualitative ethnographic approaches and quantitative social network analysis, showing the diversity of uses, the multiplicity of blogger's carreers and the plasticity of the public space.