As long as it's a fairly recent question, most of the 'regulars' probably check back every so often to see if the poster has asked any subsidiary questions (or to to see if someone has 'rubbished' their post!). I check two or three times each day, on all of the threads I've contributed to in the last day or two. Once a week, I'll probably check back for a fortnight or so.
Additionally, plenty of posters use the 'Subscribe to this thread' option. (The only problem is that it doesn't always work, which is why I don't bother with it). So it's always worth posting on your original thread, to see if you get a response.
Other than than that, there's no way of contacting a particular AB member, other than using the search facility to look for one of their recent posts and (while offering an apology to the creator of the relevant thread) trying to make contact via that thread.
Chris