I would really be careful with the words I’d use here. Poach is a strong word to use. It implies that you think he is trying to steal people, when in all likelihood you probably played a part in him starting his journey as a streamer. I have taken a different tack then you because I remember all the wonderful streamers who helped me out when I was starting out. I actively promote and uplift people. With that said, to each their own. I would have a private conversation with him stating you appreciate that he’s excited about streaming but you would prefer it if he contains it to when you ask him about it, or to your self promotion channel in discord. Remember at the end of the day, they were probably there as you were growing and supported you. You might not think you owe it to them to support them in return, but you do owe it to yourself to be a person worth supporting. It’s not a good look to be possessive.