finding a member in the membership list of active members???

Under Go you see member directory. When opened you will see at the top right page numbers which looks like Page 1 2 3 4 ... 507. Put the mouse arrow on the dots and a page number will come up so click. A bot of trial and error to get the group of pages where the member's name will be.

Also, go to a forum where you know where he posted and with find enter his user name. That can find posts he made and also his user name in posts, usually under quotes. I use this quite a bit for myself. Since I have a long history of being banned on AR I have posts under different usernames. One of then was from about 2000 to 2006 or so and I often search on it in Big Bores forum to bring up old threads I like to look at.