The only exceptions would be when (1) the information provided is false and the person providing the tip has the appropriately standard of intent1 in providing the false statement (which can be actionable as defamation or intentional interference with contract as the DJ suing Taylor Swifts alleges in the Mueller v. Taylor Swift trial pending right now), or (2) the person providing the tip was someone who owed you a duty of confidentiality (e.g. your lawyer or psychiatrist), but that duty applies only to confidential communications between you and that person in most cases, and hence not to Facebook posts.
1 To the extent that you are not a public figure and this is not a matter of public concern, even a negligent misrepresentation about what you actually wrote on Facebook, that is not a statement of opinion and is not accompanied by a reference allowing someone to confirm the accuracy of the statement at the source, could give rise to legal liability on the part of the person giving the tip. The standard of intent is the higher "actual malice" threshold for statements on matters of public concern, statements by media defendants and statements about public figures. But, there is nothing in the question to suggest that the tip given was in any way inaccurate.
This Does Not Legally Constitute Harassment
For example, if the person providing the tip sent an email about that tip every five minutes for several days to every email address at your employer, causing your employer to find that it was just too disruptive to the employer's business to keep you on the payroll, that might be harassment, but that would have nothing to do with the content of the message provided in that case.
Similarly, if someone screamed and yelled their statement over a loudspeaker every time you tried to tutor someone, that might be harassment, again, without regard to the content of what they were saying. In those cases, the "time, place and manner" exception to laws limiting the freedom of speech would apply.