Help, I can't search from the App Launcher anymore
Run this in your Terminal to clear the Launcher.

sqlite3 ~/Library/Application\ Support/Dock/*.db "DELETE from apps; \
DELETE from groups WHERE title&lt;&gt;''; DELETE from items WHERE rowid&gt;2;" \
&amp;&amp; killall Dock


When this is done, you will have a marvelously blank Launchpad interface, so to add your applications again all you have to do is drag them to the Launchpad icon in the Dock (drag the Launchpad program itself from the /Applications folder to the Dock if it is not already there). Any new applications you purchase through the Mac App Store will be automatically added to Launchpad.

Be sure to back up the database file before you alter it by copying it to your Desktop or another safe location. If for some reason you have messed up Launchpad and wish to restore your previous settings then you can restore the backup (or even use Time Machine to restore a previously backed up database file) and then log out and log back in to your system.

Alternatively, if you wish to reset the Launchpad to its default settings and organization, then all you need to do is delete the database file. To do this, press the Option key and choose Library from the Go menu in the Finder, and then navigate to the /Application Support/Dock/ folder and remove the ".db" file (it will have a long string of letters and numbers as its name). Or you can run the following command in the Terminal:

rm ~/Library/Application\ Support/Dock/*.db


Source: http://www.cnet.com/news/how-to-reset-and-manage-the-os-x-10-7-launchpad-interface/