The app shows who unfriended you since you installed it, not before that.Simply log in and press "synchronyze friends list". Wait for your friends list to be imported and you are all set up. It will notify you if someone deletes you, or even if some friend deactivate / reactivate his profile. It is still a good idea to sync your list manually sometimes from within the app. You will see how many friends you added or lost since last time you checked. Press the "more information" button and check the list of all the friends you added or lost since you installed the app. Also check the currently inactive profiles of your friends.