Beside seeking the person out, I don't see what's totally unrealistic about it. Here's the most realistic scenario I can come up with:
Somebody posts a suicidal note on a forum as large as GAF. Out of the hundreds (if not thousands) of people who read the post a couple of genuine people respond in a sincere way to it and offer help (e.g. a mere phone call). Their response could be fueled by personal experiences, for example. That reaction starts resonating with other people, and you know how many attention whores and me-toos are out there, so the circle of support expands.
That, imo, is the least I expect from a crowd as large as GAF's. It's just statistically impossible that not a single person would offer to help in any way, out of all of those people.