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.
Debt secured by a principal residence or second home to the extent of the excess of fair market value over acquisition debt. An interest deduction is generally allowed for home equity debt up to $100,000 ($50,000 if married filing separately).