Pro bono work is usually to take someone with limited money OUT of a bad situation, for example help abused foster kids petition for being placed in a new foster home, or help an illegal immigrant from being deported with their children.. not "punish a CEO committing fraud to people earning 6 figure salaries".
On the other hand, the right government contact (police? employment? ) will be happy to go after the scammer for "free".
Now that you mention it, is it even allowed that someone outside the DAs office try criminal cases? The DA is the legal representative of the state in that case, and I don't know if someone else can just step in there.
The concept of "private prosecution" exists, but my understanding is that it's not usually practiced (anymore). Some states prohibit it completely, and of those that do allow it some judicial authority is still usually required to sign off on it before it can proceed.
On the other hand, the right government contact (police? employment? ) will be happy to go after the scammer for "free".