If they have started using their account, they will appear in the User List's [In-use users] tab in the Admin Settings. If they are not an active user, where their name is listed depends on whether or not they already had a Chatwork account when they were added as a user.

 

If they already had an account when added as a user:

If they are not an active user, they are listed in the [Unregistered Users] tab.

 

If they did not already have an account when added as a user:

If they are not an active user, they will appear in the [Pre-Login user] tab.