It's not just about Instagram. The second this post went up, every major news outlet reported on it. Tonight, this will be the lead story on all the nightly news broadcasts. It's already all over Twitter, all over Facebook, and all over TikTok.
Every local affiliate and newspaper will also be broadcasting/writing about this.
I get your point with focusing on the outlets in the immediate area and surrounding regions, but you're going to have a similar result, only in reverse.
There's a ton of resources on this, and law enforcement knows how to prioritize tips, ie, people saying "I saw this online," as opposed to "I saw this that night."
The latter is what they'll focus on.