Apps, even after being removed from the Launchpad or Applications sidebar in Finder, do leave preferences and other files scattered around. Where are they, typically, and how does one find them?
The short answer is that preferences and other files are usually in these locations:
~/Documents~/Library/Application Support~/Library/Caches~/Library/Containers~/Library/Preferences/Library/Application Support/Library/Preferences/tmp
Here ~ is simply a shorthand for your user folder, e.g. /Users/username. So, ~/Documents and ~/Library are user-specific (i.e. part of the user domain), while the rest are applicable to the current computer (local domain). More information can be found in the Mac Developer Library under File System Basics.
Preference files have the extension plist (Property List). As always, be careful what you delete!
Terminal
If you are using Terminal, you can use find and mdfind.
To search a given set of folders for a matching filename (case insensitive), use the command below. In this example, I'm searching for VirtualBox files. The 2>/dev/null is just to eat errors like "Permission denied". And, one could even delete all the files found by adding -exec rm {} to this one command... but I really, really would NOT do that if I were you!
find ~/Library/Application\ Support ~/Library/Caches ~/Library/Containers ~/Library/Preferences /Library/Application\ Support /Library/Preferences -iname "*virtualbox*" 2>/dev/nullAlso, there is the mdfind command to search the Spotlight indexed files and metadata, including the folders above (also case insensitive), e.g.
mdfind virtualboxGo To Folder
If you prefer to use Finder, you typically can't see or search system folders like those above. It's possible, just not obvious. Also note, Finder is not case sensitive.
From the Finder menu, Go > Go To Folder... and type in name of the folder as listed above.
Finder Search
Type in a search term, e.g. a partial filename like plist, making sure "This Mac" is selected. Then, hit the tiny + button just under the search input field.
Set the first field to Other... and select System Files.
And the second field to are included, so that you land up with this:
Now your search will include these typically hidden file locations.