We have seen that even when it is clear to someone that one person has wronged another financially, he may not attempt to effect justice outside the confines of halachah. This applies not only to a witness, but also to the victim himself.
If one feels that he has fallen victim to another person’s dishonesty, and after verifying the facts concludes that he has a valid claim against that person, he must not publicly speak against that person for the sake of attaining restitution. Rather, he should confront the individual privately and, if necessary, consult a rav. If possible, the name of the accused should not be mentioned.
A witness may not divulge to the victim the identity of the perpetrator, if the victim could be expected to employ halachically unacceptable tactics to retrieve his money.
Sefer Chofetz Chaim. 7 Kislev, Page 182