I put some money into the investment app "stash" but I have not withdrawn any of that money. Do I have to report what I added to the app even if I don't have any income?

No, you only enter investments when you sell them. However, Stash Invest accounts are taxable brokerage accounts and you are required by the IRS to report income earned from capital gains and other applicable distributions. Each year, Stash will send you a tax statement so that you can file your taxes appropriately. In general, if you hold your investments for longer than a year, you will avoid paying short term capital gains taxes. Additional information: What tax documents should I receive? | Ask Stash

Some forms your may receive:

• When you sell an investment, you generally receive Form 1099-B - IRS.gov .
• When you receive interest, you generally receive 1099-Int - IRS.gov.
• When you receive dividends, you generally receive 1099-Div - IRS.gov