Can I tell a kid in our friend group to find new friends?
Why do you want to tell him to find new friends? It sounds a bit cruel.
He is ruining the fun for everyone.
That's really mean. Think about how hurt he will feel if you tell him to find new friends. Be nice and include him in your group of friends.
I wouldn't really care if he's sad. It's what he deserves since he's nothing but a bitch.
If he is that problematic and troublesome for your friend group, then I guess he is not a proper fit and you have the right to ask him to leave. Just be nice about it. There is no need for aggressive tactics because that would create extra drama.