[Variol (Farseer) Elmwood]

I'm leaning toward the phone call. 'Course, sometimes it's easier to say than do.
We have seen a number of situations were things posted online become reality and people get shot and killed.
Could inappropriate sexual talk/text because action?
What's going to become "normal" text for the children who read this stuff?
I recommend the Matthew 18 (15-22) thing. It's a little different, but worth considering.
I would even consider having your son approach this boy directly first. I know he's only 9, but it may be good for him. Of course though, that's between you, your wife and son. I think it's good for him to know that you are seeing this stuff. You are the parent after all. It's the same as keeping up his grades and all the other parenting stuff.
Being a "non" parent, I can't speak into it too much.