You need to go to the Team project and add some users to your team. If you first select Team Project \ Team, you will notice that you have “Members (0)” on the right. If you click Manage All Members under this heading, you can add any number of Windows or Microsoft Id users to this list.

Now that you have added users to the team, if you also select this command in Visual Studio, you can select any of these users to view. This list is actually all users who have "Contributor" permissions for Team Project, which are provided using the above process.
, Foundation Server 2013.