Depends on when the last time they were posted to. The threads with the latest posts are at the top of the screen were as the older ones get pushed further down. They could also be on the 2nd or 3rd page. You could also select "Subscribe to this Thread" from the thread menu and that way it will be in your list of subscribed threads.
Can you explain why many of the sweepstakes disappear even tho they aren't expired? In particular, I have to search for the Staples and Cheer every day, as they have "dropped off" the list. Shouldn't the current ones stay on the main list?