friends and families have even called the police in some cases and they take no action. It feels like the police actively ignore this stuff

I'm going to be a little glib here : Just fix this part and you won't need to scan social media posts.

Also, once this is in place you'll find that the majority of perpetrators - the ones who plan things out - won't post super incriminating things beforehand and their generally-disturbed posts will be lost in the sea of general discontent flagged by an algorithm trying to sift the wheat from the chaff.