When we are dreaming, in reality, we are all astral projecting you could say. As for finding your friend, this is possible but he may not remember it if he is not lucid within the dream. He may remember bits of it, but not fully as when you encounter other people on the Astral plane they may seem distorted. There is no danger of Astral Projection, you are connected to your body and nothing will affect your physical body in any way. As to how, there are countless methods to achieving AP as you can imagine, you just need to find one that will suit and work for you. Here is a website that may come of use:
Hope this helped! Good Luck!