I understand why almost all of the users replied that parental negligence is a major factor why this has happened, and I would also agree on that. Regardless of the busy schedule, distance, the age of the children, your siblings and basically anyone in the family, parents and other family members must check on one another from time to time. A simple how are you could make a difference, and even more advices that would leave an impact on them to have realizations on the things that they are currently doing. Depression is proven to be diagnosed, but it is not something that can be just easily determined, thus its cure would be a collaborative effort of the experts and the patients themselves.
You got it right there, somehow I feel like you're a parent now, aren't you? Well, that doesn't matter some are good at advicing when they aren't on that position (pun intended). Not a parent yet but I totally agree that's still on the parents to blame even the case isn't directly pointing at them. I've seen how we grow being disciplined over things and I just realized right now how lucky I've been grounded when I did wrong.
Can't say for sure about depression but it's really dangerous as a cancer, if the case from the OP was pointing at depression then the blame was still at the parents. I just can't help but think how they regret this tragic event to bury their own child, though that wouldn't change at all for them but to those who are still gonna save another child with the same scenario. This should be an eye opener to anyone especially if they're a parent, I am reminding myself as a future parent.
It’s also important here that almost all children now have smartphones, and you still won’t be able to constantly control what they do on the Internet, because for this you must constantly be near the child. But this is impossible.
I see only one way out here, do not buy a smartphone for him until the maximum possible age. And limit yourself to a primitive phone only for voice communication and SMS and without access to the Internet. But I understand that such a child can be an outcast among peers, which also complicates the task.
In short, the most difficult problem of our time.