I was removed from the sex offender list by the state in May because I don't have a sex related crime, but I can still find myself posted on websites and posts labeling me as a registered sex offender. Can I take legal action?
Can I sue someone for publicly calling me a sex offender if I'm not one?
Yes. However, in this particular case you need to take a preliminary step regardless of your jurisdiction, which I assume is somewhere in the U.S. Prior to filing any complaint (and I will repeat this below), it is in your best interest that you demand a retraction and removal of the defamatory falsehood. Be sure to show the prospective defendant(s) some proof that supports your pre-suit demand.
You need to secure your ability to prove in court that you made that demand. For that reason, your requests should be in writing (email, and certified mail if practicable). If it is not by email, you should have the addressee at least sign a receipt copy of your demand letter.
A demand of retraction is prerequisite in jurisdictions such as Texas and Florida. If you [or your lawyer] omit that step, the court will easily dismiss your complaint altogether. In other jurisdictions, such as Michigan, the request of retraction is a requirement only if you intend to pursue exemplary and punitive damages. See MCL 600.2911(2)(b). Regardless of the jurisdiction, your request or demand to each prospective defendant needs to be made prior to filing the corresponding complaint/pleadings in court.
Even if your jurisdiction does not have that prerequisite, failing to request a retraction and removal of the defamatory falsehoods would allow the defendant to justify itself and/or obtain leniency on the basis that it was not aware that the registry information turned out to be disproved/inaccurate.
In your complaint(s), you will pursue injunctive relief that consists of ordering the removal [from each website or post] of the defamatory falsehoods. It is also reasonable for you to also ask for monetary relief.
You certainly have a claim of defamation per se, but a ruling granting you an award of substantive damages is doubtful unless the defendant refuses --or neglects-- to remove the inaccurate records. If the website owners/authors promptly remove the false records, it is going to be difficult or impossible to prove actual malice: that is, that they published the falsehoods (1) despite knowing them to be false, or (2) with reckless disregard of their truth.
Without the ability to prove actual malice or that you suffered special damages (whether it is a loss of employment or other economic damages), the court would only grant you nominal damages, which is the negligible amount of one dollar.
Lastly, beware that even the granting of injunctive relief might be ineffective. I [vaguely] recall a case where federal court ordered a removal from sex offender registry, but apparently the defendant ignored the order. I have no idea how much the plaintiff's lawyer charged him for the futile representation, but the last time I checked neither the problem was fixed nor did it appear that the attorney pushed any further to ensure compliance with the order. I will not disclose the name of the lawyer, since that would facilitate the unintended consequence of identifying the defamed plaintiff.