Here is the simple trick to find the friends who are online in google talk but appearing offline.
Follow these steps to check who all are in invisible state.
- Open the chat window by clicking your friend’s name
 - Click you friends name and select “Go off the Record”.
 - Send some message to that user.
 - if you get the feedback from GTALK that “User is offline and can’t receive messages” in red color means that the user is really offline.
 - But if you get no response that means that the user is appearing offline and in invisible mode.