This paper presents a social network-based peer-to-peer search service for identifying right collaborators in the context of Web 2.0. We present a three-layer hierarchical social network, in which we identify two important relationship ties - knowledge relationship tie and social relationship tie. These relationship ties are metric used to measure the collaboration strength between pairs of participants on a social network. The stronger the knowledge relationship tie, the more knowledgeable the participants; the stronger the social relationship tie, the more likely the participants are willing to share their knowledge. By analyzing and calculating these relationship ties among peers using our computational model, we propose a systematic way to discover collaboration peers according to configurable and customizable requirements. Experiences of providing Web 2.0 services for identifying communities of practice through peer-to-peer search are also reported.