Successful software projects require engaged collaborators interacting with each other across the entire development life-cycle. Unfortunately, for social coding platforms, e.g., GitHub, identifying a suitable collaborator to strengthen their ties and improve their engagement in the project is challenging, given that reliable information for collaborator identification is often not readily available. In this work, we propose and evaluate a collaborator recommendation tool - COOP FINDER - to help developers find collaborators in a specific project based on similar interests related to co–changed files. We design our Web prototype–tool using visualization techniques. As a result of the preliminary user study, we observed that 95% of the participants had positive impressions of the tool. Furthermore, 75% of participants stated that they would use the tool in their daily lives or recommend it to others. Repository: https://github.com/kattiana/coopfinder;