We report on results of a study examining the formation of teams around newly registered open source software development projects on SourceForge.Net. We found that project leaders affected the likelihood of attracting developer interest through project management involving early code release and maintaining high levels of development activity. project leaders exhibited varying levels of openness towards new volunteer developers joining their projects. Leaders' decisions regarding developer joining had a direct impact on project team size - an important factor determining a project's likelihood of attracting new developers.