What about offering more perks/options for whistle-blowers? I suppose the financial gain of whistle-blowing something like this is rather low... while the person will likely be barred from working at a lot of places (referring to an article on the Frontpage here a few days ago).
The financial gain of whistle-blowing something like this is pretty comparable to the societal value of whistle-blowing something like this. One random Facebook employee (of unknown rank and seniority) called a kid a whale; that doesn't matter in the slightest beyond its impact on an existing story. We can't incentivize people to run to the media with every chat log that looks bad out of context.
Really I think what is needed for that are far more robust protection against blacklisting of whistleblowers - although the devil is in the details given the general difficulty of proving employment discrimination.
If they couldn't keep their ethical fences up we would see far more impact from the same numbers of whistleblowers - criminals think they won't be caught.