I’m so sorry, shockvalue, that this happened to your friend. There is always an extra measure of grief when someone young dies, because we mourn not only their loss, but the loss of their potential.
We can talk with you about our own experiences, but each person walks through grief alone.
Be good to yourself as you grieve. Make a point to get enough sleep and to eat even if you don’t feel like it emotionally.
As AlfredaPrufrock mentioned, sharing memories and grief with others who are also mourning can help. That is how our rituals of funerals and memorial services developed. They are not so much for the dead, who are beyond the need for that, but for the living, so that we can remember and celebrate the person we lost and the place they held in our hearts.
Maybe you two had a special place you hung out. You could go there and remember your friend too.
When I lost my sister, I got comfort from talking to her about what was going on.
If you are up to answerjill’s advice, a note in a card to his family, even, will be of help to them (and doing that may help you). What to say? Something about how knowing your friend that changed you or an anecdote or particular trait he had that you will always remember.
Finally, grieving does not mean perpetual sadness. It’s OK to laugh with friends remembering the goofy things your friend did. It’s human and natural.