You may be able to claim a loss on worthless stock if the stock became worthless in 2016. From the date of the letter, though, it seems like the stock became worthless in 2015.
You would report this as a Sale of Stock in the Investment Income section of TurboTax.
If the IRS questions you, you should be able to establish that the shares are indeed worthless, and the year that this occurred. Please see the following for more information.
https://ttlc.intuit.com/replies/4789435
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