Can I write off the money I paid to buy into the restaurant I’ve been working at?

[AnnetteB6]

No, not until you sell your investment in the restaurant.  

Keep a record of the amount that you have invested and when you made the investment.  Then, when you sell your 'shares' of the business, you will report your income and the amount that you invested.  At that point, you will either have a taxable gain or a deductible loss.

Depending on what type of arrangement has been made with your investment, you may receive a K-1 from the business to report your portion of the business income and expenses.  That K-1 will be entered as part of your tax return.  Expect a K-1 if you are considered a partner in the business partnership based on your investment.