If you bought the time share for personal use, then just as in the case of a sale of a principal residence, no loss is allowed. If you bought the time share for investment purposes, you may be able to take the loss as a long-term capital loss.
Casualty losses such as from a storm, in areas declared by the President to warrant federal assistance. An election may be made to deduct the loss in the year before the loss or the year of the loss.