How long has it been since the sweepstakes ended? Check the rules, they should tell you when the prizes should be shipped, normally 4-8 weeks after the end of the sweeps.
The rules should also give you the sponsor, write them if it has been longer than the stated time frame.
:sunny: Postopia is one where you have to download a form (it's an instant for minors) must have parental approval. Did you send the paperwork in? Did you keep a copy? The address should be on your paperwork.