Does anyone know how to search for all the threads created by a particular user? This feature used to be available in the old website, but I can't find it in the new, improved one.
Are you looking for the user that created the thread? Or the thread created by a user?
AFAIK if you are seeking a thread which you know the user you can locate all it through their profile if they allow access to it. (some have disabled the ability to go through history of posts).