Hello Kristi. Placing a new ad should not eliminate any previous ads that have not yet expired. You will receive an email notifying you of any expiration -- click the link in the email -- not much will seem to happen but that's the way the software is built. It's kinda kludgy but it works.
I would most strongly suggest that you rely on members contacting you through AIR Forums member contact and edit/remove your email from the public ad. Web bots scour websites looking for obvious email addresses in the format email@example.com
-- and then Katy bar the door for all the spam you will be inundated with after that!
Back to disappearing ads... Yes, I seem to see only one from you right now. Are you starting new ones when signed in at Classifieds by clicking 'Place an ad' at the upper right on the menu bar?
I just put up two test ads and they both appeared properly.