post on (something)
1. To share information on a public place, thing, or platform. He spends so much time posting on social media that he has started letting his relationships in real life deteriorate. You should try posing on the notice board in the post office—I've seen a lot of great services advertised there.
2. To share a particular piece of information on a public place, thing, or platform. He posted some pretty inflammatory comments on Facebook over the weekend. We're posting pictures of our missing dog on buildings and lampposts all over town.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
post something on something
to fasten a notice onto something. Please post this notice on the door where everyone will see it. I will post this photo on the bulletin board.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.