Rent it out (or try to rent it out) for a couple of years first, dont use it yourself, report the rental business on your tax return, and then if you sell it for a loss, you may be able to deduct the loss. However, the loss would be measured with reference to the value of the timeshare when its use was converted from personal use to business use, so unless it were to further decline in value, there would be no loss to deduct.