ANSWER - I can think of no one simple working that would give you a definite answer. However I have three suggestions that might help you. I will add the caveat that if you are not used to working with magic and putting protections in place, working on the astral would not be something I would advocate as you rather do need to know what you are doing to keep yourself safe. I'd also say the same for working with spirits - if doing so is unfamiliar ground for you it might be best left alone.
1. Looking for another living soul on the astral plane. Leaving your body is actually more common than you would think and it is the belief of some witches that most people
travel outside their body but that it is more usual to do so subconsciously, for example while dreaming. Travelling on the astral is quicker as the only constraint is that of your mind. If your focus is to find x (in this case your friend) you do not need to know where x is. This is where astral travel differs from actual travel - you don't follow a linear path to your destination, you project to where you wish to be. Searching for your friend in this manner would certainly give you a good idea of whether he is alive or dead)
(I'm not going to give you an indepth how to guide on astral travel here. If its new to you, I'd leave it alone. However there is a good link here which will explore some of the basics and give you some background on astral travel and what it involves.)
2. Contacting the dead. My first suggestion assumes that your friend is still living but if he isn't and he is in fact dead then contacting him via the spirit world might make more sense. This is also much simpler as contacting a spirit does not involve you leaving your own body. You don't need any fancy tools though I personally favour the Ouija board as it makes for simpler communication. Don't rush out and buy one, a piece of paper with the alphabet written on it will do the trick. And read this before you do anything - a some basic protections.
Of course there are also many mundane steps you can take. These days the internet has information on just about everybody and a quick search will usually yield what you want. Have you checked out the big social media sites? Residential search on last known property? Completed a search on mutual friends? Educational establishments? Last known work place (I'm betraying my encyclopaedic knowledge of stalking here aren't I...)