Social networking service is one of major technological phenomena on Web 2.0. Hundreds of millions of users are posting message, photos, and videos on their profiles and interacting with other users, but the sharing and interaction are limited within the same social networking site. Although users can share some content on a social networking site with people outside of the social networking sites using a public references to their content, appropriate access control mechanisms are not supported. In this dissertation, we outline a cross-site interaction framework and identity mapping approaches that enable social network users to share their content across social networking sites. We propose a cross-site interaction framework x-mngr, allowing users to interact with others on other social networking sites, with a cross-site access control policy. We also propose identity-mapping approaches that map user's identities across social networking sites. The partial mapping approach based on a supervised learning mechanism which provides user's identity mapping based on a training set composed of a small subset of the profile mappings. We provide mechanisms to enable users to fuse identity-mapping decisions that are provided by their friends or others on the social network. Furthermore, we propose a Game With A Purpose (GWAP) approach that provides identity-mappings using a social network game. The proposed framework and game are implemented on real social networking sites such as Facebook and MySpace. The experiments are performed to evaluate the feasibility of our approaches. A user study is also performed and the result is included as part of our evaluation efforts for the proposed framework.