Finder not searching files in ~/Library and /Library I am using a Macbook Air with macOS High Sierra. 

When I install a third party application and later delete it, I have to remove files stored by it in Application Support, Preferences etc. in ~/Library. I have to manually look up and delete files containing the name of the third party app (eg. com.EaseUsMobiMover installed by MobiMover). 

Why doesn't Finder show these files when I search for them? And how do I make Finder search for all files containing the name of the app like com.abc for the app "abc"?
You have to include "System Files" in your criteria to search places like the user Library.



To do so, open a search window in Finder cmdF, click on "Kind" and select "Other" and scroll down to "System Files".  Tick the box under "In Menu" for easier access in the future by including it in the search menu.
(You can also specify hidden files here, with the "File invisible" attribute)




You can also save those search criteria and add them to the Finder sidebar for quick access.



If the above does not yield the desired results, a rebuild of the Spotlight index might be required.