I would say how he ended up here matters a lot, and will determine how you or anyone else talks with him. Here is my story about nihilism, in which I hope it will be clear that how I ended up there was directly related to how I found my way out.
I struggled with nihilism for nearly 20 years, starting when I was young. Early on I felt like life wasn't worth living, and later began to analyze life from a rational, evidence-based perspective. That perspective reinforced my nihilism. Now, I was also depressed off and on during all of this time, and saw doctors and therapists of various kinds and tried medications of various kinds. Not a piece of it did anything. Drugs blunted the ability to feel the emotion of despair, but the rationally drawn conclusion of meaninglessness remained. By and large, the therapists weren't smart. They were unable to engage me intellectually, were overly positive about the direction of life (which made no sense and frankly still doesn't), and seemed focused on what I would call "yes, but's." The foundation of meaninglessness didn't begin to crack until I started exploring eastern meditative practices and stumbled on the Buddha's postulate about the nature of existence "Life is suffering." It certainly matched the conclusion I had drawn about life. That was maybe 10 years ago. But still, I struggled with nihilism. Beyond the normal sorts of suffering that people endure like wishing you had more of X attribute, I wasn't suffering too much at the time and managed to muddle through. That all changed when I became faced with actual suffering. When the physical body, the thing that appears to be YOU, begins to break down it puts your values and your character to the truest test. I simply fell deeper into despair, having a foundation of nihilism. Wrapped up in this, and something that I didn't realize until later, was how I used to view goals. I saw a goal as an end. Here is this thing that I want, and I'm going to do these things in order to get it. I saw the "getting it" part of the goal as the desirable part, and it is to some degree. The problem I was noticing was that every time I would achieve a goal, I would get the thing I wanted and feel good for a little while. If it was a small goal maybe I'd feel good for a few minutes, a really big goal I'd feel good for a few days. The problem was that, inevitably, that feeling would DIE, and I would be left with the suffering and the negative emotions that I was forced to deal with. The conclusion I drew was that goals were pointless. There was never one goal that I could set such that when I achieved it then I would finally be DONE. That all fed right in to the nihilism. Another thing that I didn't realize until later, was that at the time I was very happiness focused. My goal for life was to "be happy." Sounds a lot like what many people consider. We choose a particular career, a significant other, a hobby, etc. because "it makes us happy." The problem was, happiness never lasted. No matter what I did, no matter who I was with, no matter what goal I achieved, I would always end up feeling bad. Nihilism, nihilism, and more nihilism. The cool thing is, I'm not nihilistic anymore.
I still struggle with some stuff, and who wouldn't considering the nature of how life can be. The difference today is that I no longer despair. That may be an initial reaction, but then the courage to face whatever the issue is kicks in. I started to turn everything around when I was listening to the Joe Rogan podcast back in November of I think 2016. So, it was close to two years ago. Rogan's guest that day happened to be Jordan Peterson. I didn't think too much of it but the dude sounded like he had some intesting ideas, so I went looking for his stuff on youtube. I ended up watching a lot of his stuff, including his entire maps of meaning lecture series. It gave me some interesting ideas, but things were still percolating. My starting point was that life sucks, it's awful, I can't do anything about it, and none of it matters anyway. Peterson's suggestion was, maybe you CAN do something about it, even if it's small. Some time later, I actually took a stab at some improvement in my life. I set some very very small goals (like get X, Y, and Z done today) and accomplished them. I felt good, but this wasn't feeling good because I accomplished the goal, it was feeling good because I COULD ACCOMPLISH GOALS. That's when the switch started to flip. I started viewing goals differently. Goals were not an end or a means to the end of happiness. Setting goals, even small ones, were a way for me to demonstrate to myself that I could actually do some things. What I also realized was that when I did some things, THINGS ACTUALLY GOT BETTER. I still had to deal with crap and still do, but that's not the point. The point was, that no matter how bad things were for me at the time, if I do some stuff, even small stuff, things could get a little better. More importantly, not only could things get a little better, I was ACTUALLY CAPABLE of doing some things. Never underestimate the ability to demonstrate to yourself in a compelling way that you are actually competent and capable of something. An interesting way of thinking about depression that I heard somewhere is the following. There are two lower types of depression (essentially). They have to do with the conclusions you draw. The lowest form of depression draws the conclusion "I can't, and no one can." Above that is the form of depression that draws the conclusion "I can't, but maybe someone else can." Rising above depression is courage, and the conclusion from courage is "I can." "I can," even in the smallest way, has made all the difference.
Thinking more about your description of this kid, I doubt my story applies to him at all. I think the point is clear from my story that maybe you need to ascertain what his motivations are in arriving at this conclusion. What are the unconscious factors? Did he end up there legitimately? Does he constitutionally tend towards negative emotionality? Has he felt weak most of his life? Is this his form of "teenage rebellion?" Does he seem angry? Is he intent on hurting people in an emotional way? Does he feel hurt? etc. I think how he ended up here and his underlying motivation matters a lot in terms of how you talk to him about it. Some people are nihilistic because they are depressed. Others are depressed because they are nihilistic. I was the latter and trying to "fix my depression" did absolutely nothing.
