I would like to ask forgiveness for the many times I have even read loshon hora, something that unfortunately frequently gets posted, even if I did not believe it. After all, there is a sin to simply listen to it.
Of course the victim of this crime is the person(s) being spoken about. And more often than not that person is not even a participant of the forum. So asking forgiveness, even publicly, is unlikely to reach the only person(s) who can issue that mechila.
Which, of course, is the point in refraining from engaging in (listening or spreading) loshon hora in the first place, considering the extreme difficulty in obtaining absolution.