There was an experimental search tool "global search" in version 1.9. It was removed from 2.2 It was planed to integrate it in moodle 2.3. A few month ago it was planed for 2.4.

http://docs.moodle.org/21/en/Global_Search

http://tracker.moodle.org/browse/MDL-31989

I don't know, if this tool is coming soon. I find it is a very important tool.