Presumably you could buy an advertisement that would be placed here on SF.SE. There's an Advertising Info link at the bottom of the page.
That said, I wonder how people would feel about people posting info like that in Chat by leaving a comment? I'm confident there are some of us who are looking for opportunities and would appreciate being able to obtain inside info from people who already work there.
With our site being designed to preserve anonymity, its not easy to connect with someone else unless they decide to put their contact info "out there" in the text of their profile or have a web site displayed that makes them easily reachable (for some it's a large corporate site with no personal link to them); unless of course they're also well known elsewhere because of a blog, being active on LinkedIn, Github, etc.
Besides the groups others have listed, there are several SF Jobs groups and SF related groups on LinkedIn where one can post open positions. Most of those however seem to be posts submitted by recruiters.