A regularly asked question Pete.
Your advert hasn't "disappeared", but unless you're a member who donates financially to the site your ad will not appear until it's approved.
All the moderators are pretty busy, Simon in particular with business and family issues so it may take a few days.
If you read the terms of the For Sale section I think it says anyone with less than 30 posts would have FS/Wanted ads approved, but this seems to have changed when the site was migrated to new hosts. The reason for the 30 post limit was to stop someone just joining in order to post adverts, be they genuine or bogus.
