Depending on how old it is, the thread might still be in the main subforum. I still haven't gotten around to moving all old completed threads to the Archive. You could search through the main subforum if you have an idea of how old the thread is.
The threads that contained the information on Fanfiction of the Month and Fanfiction of the Week have been moved to the Writer's Lounge. So if you want to find them, they're buried in the archives there. Also:
FFotM and
FFotW. There's both threads, so you can save them without having to search for them.
FFotM ended due to me not having the time to read through all the fics posted during the month and picking the best one. (I was the only moderator at the time.) It also ended because there were a few spats of drama involving it, and it was just easier, and more wanted by the current active community, to turn the Archive of Fanfiction of the Month into a general Archive so older stories could get read and reviewed.
Hope this helps.