OK in the year the stock became worthless show the sales price of $0 (if that is what you got) and the date it became worthless. You will enter your purchase date and the cost of the stock and then TurboTax will compute your loss on the stock.
In your TurboTax go to:
Federal Taxes
Wages and Income
Investment Income,
Stocks, Mutual Funds, Bonds, Other
For your tax records keep information that the stock has become worthless.