Selling a Nissan sentra still financed?

On February 2011 I purchased a sentra 2.0 for 17000 my down was 4000 an to now I owe under 9000 I can't pay off this vehicle because a financial hardship how or where can I be able to sell or trade this car? I went to Carmax but they said I should atleast b driving it for atleast 3 years before I intend to sell it! Anyone any advice. Definitely would Wana get rid of it an atleast get some type of cash back.