How to search Library on Mavericks Before updating to 10.9 I frequently deleted all the small files some apps leave behing by searching for invisible system files. Now it doesn't seem to work, I can navigate to the file manually just fine, but it doesn't show up in the search. Is there a way to index Library?
Are you searching via command-f within Finder? If so, do you see a pair of dropdowns that say Kind is Any? Click Kind and select System files. Any will change to aren't included. Click it and change it to are included.

If System files isn't available in the first dropdown, select the last item, Other…, and find it in the subsequent popup. 

If no dropdowns are shown, click the round + button on the right edge of the Finder window, near its top. 

If you're searching via Menubar > Spotlight, I've looked in the past for a way to include hidden files in its search results, but to no avail. 

Personally, I use App Cleaner, by the way, to tidy junk left by messy apps. 

ADDENDUM: 

I see now this works for most Library files, like those found in Application Support or Internet Plug-ins, but it fails specifically for .plist files found in the Preferences sub-folder. Not sure why Apple would do that. 

Others have had this difficulty, too, and they've solved using App Cleaner or a similar third-party app: 

http://lifehacker.com/5711409/how-to-search-for-hidden-packaged-and-system-files-in-os-x
http://forums.macrumors.com/showthread.php?t=1599438
http://hints.macworld.com/article.php?story=20121101064200135

It seems the options are third-party app, manually search through Finder, or perhaps grep through Terminal. Regardless, remember to leave http://www.apple.com/feedback/.