Sefer Chofetz Chaim chapter 10 halacha 4 footnotes 14-17

The positive use of telling others about a person who humiliated someone else besides making an impression on other how bad it is to embarrass others or to potentially convince the perpetrator to apologize, besides that there is a great benefit that can come out for the victim even if he doesn’t get any money out if the deal, which is other people sympathizing with him which will make him feel better.

Now, you might think that only for the purpose of helping the victim can you tell one person at a time what happened but if you want to spread the word to create awareness of the severity of the sin or to get the perpetrator to fix his ways then you need to tell people in groups of 3 or more, that ensures it will spread and shows you are doing it for the right reasons and not for your own benefits, however in this case where you already tried rebuking the guy and it didn’t work you don’t have to tell people in groups, you can tell them about the severity of the crime individually and you won’t look like you are doing it for ulterior motives other than to spread the truth.

The Chofetz Chaim wasn’t sure if you are just spreading the word for the sake of warning others not to follow in that path whether you are allowed to do that with name dropping in a case where it is possible that the perpetrator my have an excuse, for example he didn’t know any better or didn’t realize the severy if his crime, then maybe you can’t say any names.

And when the Chofetz Chaim said you should tell others of what happened without first telling the victim that us only if telling other won’t have any monetary repercussions for the victim but if it does then you can tell others before telling the victim.