Maybe you should sue them all for slander, libel, and defamation of character.
[In accordance with the Avvo community guidelines, this communication does not constitute "legal advice", nor does it form an attorney-client relationship.]
Well now you know that nothing on the Internet is private. If you have something to say to someone, don't post it in Facebook even with privacy settings.
About your warning - most companies have procedures for going up the chain of command if you object to a disciplinary action. Read your employee handbook and see to whom you should speak to explain more about the situation.
You don't tug on Superman's cape; you don't spit into the wind; you don't pull the mask off the old Lone Ranger; And you don't get legal advice from a free Q&A page on the Internet. The above is a general statement of the law or just my opinion. I am not saying whether it applies to your situation or not because I don't know the details and youâ€™ve not hired me as your attorney.