I put property on consignment, with contract. The company went out of business without retuning my property. Can I claim these items as a loss, if so, how?

If the property was your personal property then the loss is considered to be a personal loss.  Personal losses are not deductible.  If the property was business property, used in a business to make a profit, then you could file a casualty loss on Form 4684 Casualties and Thefts.  You would deduct your loss as an itemized deduction on Schedule A, however, if you do not itemize you will not be able to deduct the casualty loss.