i think the easiest way is to subscribe to threads that i post to regularly -
to subscribe, click on "thread tools" at the top of the thread -
and then click on "subscribe"
then when you go to "user cp" the threads will be there for you
if you want to automatically subscribe to every thread you post on,
go to "edit options" on the user cp page,
and then go to "default thread subscription mode"
The chances are that if you can't find it, it has most likely been deleted by a moderator. If a mod deleted a thread, it will also delete any posts you have made on that thread.