What to do about stolen property?

A friend offered to let me store my newly bought mattress in her storage facility so I gratefully accepted. Recently I came into the knowledge that she was planning to sell my mattress and keep the money and disociate herself from me. I approached her to get back my mattress and she denied all allegations and refuses to return the mattress. Is there anything I can do legally since I have to receipt with my name on it and the serial number? Please help ASAP email me at laurabkjacobs@aol.com if u can help