His friends are great. It's like they have Kaede danger senses. Every time something terrible happens to him they're somehow there immediately no matter where he is
I'll just play devil's advocate a bit.
I mean, they definitely were not there immediately after he was raped. It doesn't say exactly when they found him, but they sure as hell didn't find him before or during the rape. They found him some amount of time afterwards.
Here, I would just guess they were walking home after school. Tsubasa had gotten out of school too, and I suppose Kaede, Izumi, and Asahi also got out around the same time because the school schedules are probably similar. So they'd be walking together when Kaede maybe sees Tsubasa ahead and then goes off without Asahi or Izumi. Then, when Kaede takes a while and they don't hear from him, the two probably look around and find him.
None of that is ever really said, but it's not unrealistic for this.
To be clear, they are great friends. I don't expect them to immediately find him. But it doesn't look immediate.