I'm not quite sure I'm interpreting the problem correctly. In this answer, I'm assuming that your son takes nude pictures of himself (because of points 2 and 7 on your list) and sends them to friends (if he sends them to random strangers, immediately stop this, if necessary by removing his ability to take nude pictures of himself, in order to protect your child!).
You've already compiled a list of problems that can result from this. But I could imagine that in your desire to convince him that what he's doing is wrong, you actually confronted him with this list, one item after the other.
Now imagine what that does. He's sharing these nude pictures with some of his friends (?), not thinking too much except that it is exciting, and suddenly you come along with all these reasons why he is doing something really stupid. Add to it the fact that he's possibly embarassed about it if you've actually seen these pictures.
I think the way forward shouldn't be to "take away the internet" - you can't possibly do this. He can get on a friend's wifi hotspot, on free wifi hotspots, can use the internet at school etc. So this is just a punishmet that won't cure the problem (to keep him from taking nude pictures of himself, you'd have to remove his access to a camera - e.g. take away his phone - this wouldn't be foolproof either, but much more effective).
If I were you, I'd start compiling evidence that you're correct in warning him of the dangers to himself. I'd leave the legal side of this to the sidelines - tell him he's possibly creating child pornography as defined by the law, so he knows he's doing something that can be considered illegal (depending on where you live) and might get him into legal trouble. But I'd focus on the dangers to his social standing and self-esteem, which he obviously hasn't thought through. Ask him what he'll do when someone who doesn't like him gets hold of a nude picture of him and posts it for everyone at his school to see. Discuss with him how his pictures might get in the hands of someone besides his friends. Explain that he can't possibly keep control of a picture he sends to somebody else. Then show him examples of what you mean - there are enough news articles about people losing control of such situations that it shouldn't be hard. There's also a nice movie about this, but it's a german production ("Homevideo") and I don't think it has been translated into english.
You write that he doesn't want to listen. You don't say why. Maybe it's because he's too embarassed to want to discuss this with you, so maybe having someone else talk to him about it might work.
If that isn't it and he's just stubborn, maybe taking his phone away until he's ready to discuss this with you might work.
If he's convinced that his behaviour won't lead to problems, maybe you could provoke a small one, in the safe environment of your family, to show him that what he's doing has consequences he will have to deal with sooner or later. Printing out one of the nude pictures and giving it to him as a physical object, asking him whether he'd want to show it to his mom, or his sisters, or his grandparents etc might start a thought-process going. You could also ask him whether he thinks you've only printed out a single copy, and how he can ever know there aren't more copies. Make him realize that this is exactly what happened once he sent that image to his friends - he has no idea what happened to it. Don't threaten to send the picture to other people, but make sure he understands that this is what might happen anyway because you're not the only one with a copy of that image, and he has basically no clue who else has a copy on their phone by now. If he gets angry at you for taking one of his pictures, use that to show him that while he didn't want it to get into your hands, it still got there - because he lost control of it. If his phone has access protection and he doesn't want to give it up to you, that's another starting point for a discussion: Obviously there are things on there he doesn't want you to see - so again, you can discuss with him how he decides who gets to see what. For example, what happens if one of the parents of the friends who received his nudes has a similar conversation with their child and gets to see his nude picture? What if that parent then confronts your wife and you with that picture... lots of good ways to make consequences more real here.
Be very careful if you try to provoke such a incident by basically bringing one of his nude pictures into your posession. I'd only do it if nothing else worked, beause it is a serious invasion of his privacy, even if you'd only do it to make him realize his privacy is more important than he thinks.
Also, think about whether to talk to the parents of your sons friends. Again, I'd probably not do this, but depending on the legal consequences of having these pictures fall into the wrong hands, it might be necessary to inform them so you can all take steps together to protect your children before something happens that will involve the police and blow this out of proportion.
