Copyright protection applies to "original works of authorship", as defined in 17 USC 101. You'd have to argue that your post was a "literary work". If it's just a straightforward statement that you are hiring, accompanied by your contact info, that might be hard to do. But if so, then in principle you could sue people for distributing unauthorized copies of your work. You would have to register your copyright first. If you won, they'd be liable for damages.
However, this only protects your "literary work" itself. The information contained in your post has no protection; only your specific expression of that information. Someone could express that information in their own words ("I heard that Ryan is hiring; his contact info is XXX") and share it with whomever they wanted, on whatever terms they choose; this would be perfectly legal and protected by the First Amendment.
The only way to prevent it would be to get all recipients of your post to agree to a nondisclosure agreement in advance.