No search results at all? Do any search result numbers show up in the Search tab?

If you see a number like 0/135 then chances are the results are considered as junk, correctly or incorrectly so you would need to adjust those files which are obviously not junk to be categorised as non junk. Go to LW's menu bar, Tools > Options > Filters > Junk & choose to show at bottom of search results. This is usually the default from memory. Select file & click trash can icon to designate as non junk or as junk.

However if no search results at all, then something is wrong. Perhaps you can go to Tools > Options > Searching & choose to show all speeds & qualities.

There's always a chance you are connecting through dud ultrapeers & getting zero results in searches back in which case you can either filter them out or else disconnect & reconnect 10 mins or so later.