You have had good advice. It is scary that so many have sex so young. My daughter is 11 and the thought of her having sex at such an early age is horrifying.
You can get hold of artificial babies that cry and require attention. They demonstrate to teens the reality of having a baby and how tiring it is. It might be interesting to give him a taste of parenthood.
He is taking a risk every time he has sex although he probably does not care one jot about the consequences. I would also be concerned about the girl if it was her first time it wouldn't have been the most wonderful experience in the world. She may be having regrets. Also he needs to fully understand how difficult it can be to get under control if a girl changes her mind and at the last minute says no. There is a great deal of adult baggage that comes with sex and perhaps it may be worth talking to him about how his actions affect the other person in the equation.
I agree that you need to establish why he did it in the first place. If it was to gain some sort of Kudos with his peers I pity the girl. Just curious is she a witness? If she is the mess will grow and grow.