AppZapper, AppCleaner, CleanApp, TrashMe, and similar apps do not do a thorough job of removing all files/folders related to deleted apps. I tested several of these, using Skype as the app to be removed. Of 17 items to be removed:

AppZapper missed 13 items
AppCleaner missed 11 items
AppDelete missed 8 items
Hazel missed 9 items

I also tested AppTrap, CleanMyMac and a few others and they all left files/folders behind. In most cases, they remove .plist files and a few others, but leave behind much larger files and folders. Even apps with uninstallers leave things behind.

The most effective method of fully removing all files/folders related to an app is here:

http://forums.macrumors.com/showpost.php?p=11171082&postcount=16