No. An investment is equity in a business. You can deduct losses, and you will have to declare any profits as income. If you dispose of this investment at a loss, that is deductible. Likewise, if you sell the investment for a profit, that is income, and taxable.
But, the investment in the business is not deductible.
You mention that you do not own the business. In that case, perhaps you loaned this money. If they made payments to you that include interest, that interest is income and taxable. If for some reason, the loan will never be repaid you could write that off as an uncollectible bad debt. Having made a loan does not create a tax deduction.
