I started a c corp in 2018, but never generated any revenues. How can I recoup my investment into the company?

If the C Corp is actively operating now, you can consider your original costs as part of your equity and an "amortizable" asset of the corporation and begin to amortize the expense of those original start up expenses.

If the business has permanently ceased to operate, you can treat it the same as you would if you had purchased stock in a public company that went out of business, as a capital loss.

To enter that loss in TurboTax, scroll down to Investment Income, under Income & Expenses and select Stocks, Mutual Funds, Bonds, Other.  

Answer the first question NO, when asked if you have a 1099-B.

For who "Brokered" this sale on the next screen, you can put your own name or the name of the C Corp.

Follow the on-screen prompts for a "Worthless Security."