I want to save him.
First of all,
you will never save him, only God can save him. However, I'm sure this was only a minor faux pas on your part and I'm sure you understand this basic principle. Which brings me to the major point of all witnessing - prayer. Prayer needs to always start every time you are gong to witness to someone. You need to pray for the Spirit to bring the words about in you and lead you to how you can witness to your friend the most effective way, and that the young person you are witnessing to, to have a heart opened and ready to receive His grace and salvation.
You want to be a witness to him via email? Have you all ever spoken of the Gospel of Jesus Christ in the past? I'll tell you a good question to ask when you are unsure of a person's belief in Christ - ask him if he attends church, of course first offer where you attend, and then ask him what church he attends. This question will open up a religious discussion, which may lead up to witnessing to him. However, DO NOT get into any doctrinal discussions, this is merely to find out if he is open to Christianity at all.
For example, I tell a friend I go to a Bible church, do you go to church? She says, no, I really haven't since I was little.
Then, she might offer something like, although I used to like church, or she'll say I stopped going because they're all hypocrites, or something like that. Well, then you say, I was just wondering, you see I became a Christian when ... then your testimony. A testimony is just that - YOUR story and this can not be rebutted. It is your experience and through your experience you can give the Gospel.
Now, that is the easiest, witnessing 101 method. Witnessing however, is always built upon your assurance in your Savior, and that He will save this person if it be His will. Doors open and close by God, not by your personal strength. "For it is by faith you are saved, not by works." That is why it needs to be grounded in prayer to Your Lord and then you yourself needs to be fairly knowledgeable in Whom you believe and why you believe.
I don't mind talking to you via pm if you like. Let me know how it goes.
I hope I helped some. ^____^