Unfortunately my cam on my Macbook is not working with the Mac App GoToMeeting (Of course the function is activated). I do not have the problem when using the service via Chrome. It also offers my functions in order to stop broadcasting my video, means that the app thinks that the cam is working. Buy the way the green light on the top of the Macbook beside the camera (which turns on when the camera is active) stays off.
You may have to allow GoToMeeting access to your webcam feed through the security preferences there. If this security check is missed during the initial installation, they can be manually enabled through this path: System Preferences > Security & Privacy > GoToAssist