Changing the ultrapeers that you're connected to can make a difference to the search results that you see - different hosts conect to other different hosts & on it goes

Keep in mind that you can't search the whole network - it's just too big.

Try varying your search terms... look for artist or album rather than song title, director or actors' names rather than movie title etc. Also try the 'All Types' search.
Search at different times of day, as people in other time zones log on & off then files being shared will change.

You might find a few more tips here: How to find music