I tried using the search on the board an it didn't work.
The search is not broken. Due to high server load, if you use a stopword in your query, you will get a blank page. This is explained in the "ReadMe Before Posting
" sticky at the top of this forum.
There is no way to do what you want in the standard phpBB, although there may be a MOD that will delete a user and all his/her posts.