Form 1099-K is issued by a payment processor, not by the person who receives the payments. A payment processor doesn't have to issue a 1099-K unless the total is over $20,000. You are not a payment processor, so that $20,000 threshold doesn't apply to you. You have to report all your income, no matter how little it is, whether or not you get a 1099-K, 1099-MISC, or any other form.
By taking money for streaming, on Twitch or anywhere else, you are in business for yourself. The money you get is business income, not gifts or donations. You have to report it as business income on your tax return. You have to report all of it, no matter how little it is. And you have to report it even if you don't get any kind of 1099 form.
The second link that SweetieJean posted, from streambig.net, has very good information. Read it.
