How to report a potential predator that works with children?

I’ve come across some alarming and inapropriate online posts from an adult man targeted at minors on social media. What is concerning is that, after some digging, I found out that this man (foreginer living in Tokyo) might be working as a teacher with children.
I’m very concerned about the safety of any child that comes in contact with him, but I cannot find any information about where to report this to the authorities if you’re not the guardian of a student.
– Could I be in legal trouble for sharing screenshots of his inapropriate posts and his face online so people can help identify him and report his behavior to his workplace? Could there be any negative repercusions if I share them on Reddit?
– Is there a hotline where you can report suspicions of child endangerment? So far I’ve only been able to report to the cyber crimes department.

by No-more-predators