From what I've read about people who joined neo-Nazi skinhead gangs, they were sometimes literally recruited by older men who would prowl around high schools and look for awkward, shy, lone males who seemed to be by themselves, not have friends, etc. They're isolated, probably hate most of the people around them anyways, and are highly impressionable given their youth.
Also having a messed-up family life is pretty common. I also knew someone who later became a neo-Nazi skinhead (I found out a few years later) and he fit the profile.
They don't have strong mentors who can transition them from boyhood to adulthood. The transition from youth to man has been eliminated, so we go straight from being a boy to a man without any pause or shift period, and the lack of mentors means youth don't learn how to deal with things like (say) violence, or deal with someone insulting you on the internet, or learn how to relate to people of different backgrounds than your own. Some people join the Marines or whatever and gain experience that way, but it's not an entirely positive one. I don't mean to sound like a conservative, because I'm not, but this was a role that was once filled by traditional institutions like scouting organizations or churches and those have also gone away, been discredited in various ways, have failed to adapt to the times. I'm not going to say those organizations were all positive, again, just that they filled a function in terms of teaching skills and discipline as a way of building self-confidence. And fascists PREY on people with weak self-confidence.
And trying to gain some awareness of the world from behind a computer screen and staying up all night browsing /pol/ is just a recipe for disaster.