It should work with the search tool at the top of the page, but since it doesn't seem to work for you, click where it says "advanced search", use the "search by member name" box. Let us know if that works.
Hmm... Try this:
Under the search bar at the top is a little link that says "Advanced Search." Click on that and start typing in their username in the box that says "Search by username." The system tries to autocomplete and gives suggestions.
Earlier tonight I tried searching for a member, and could not find them. I tried several variations and the wildcard *.
I eventually went to one of their last post and checked my spelling. I had the correct spelling.
Imp- I did find 57 others with the same letters in their usernames.