If you were from The US or Canada, absolutely. One example is the story of 12DailyPro, it was a paid autosurf running more or less on the HYIPs model. until the SEC starts investigating this Ponzi. Another one is Bitconnect. Promoting a scam is an act punishable by a justice sanction. Usually a fine equivalent to the amount you won, so you have to pay back to the courts your winnings you generated with the scam.
As other users above said it depends on the laws in your country, that's what really matter.
It is, but you have to prove that the promoter knew what he was promoting (intent). One case can be totally different from another. To visualize this I'll give you some examples.
1. The promoter took a referral link from a site that he was investing in and believed to be real, not a scam. You clicked in the link, registered into the program and lost.
2. The promoter thought it to be legit and told you about it, invited you in. You know the rest.
3. The promoter knew it to be a ponzi scheme and invited you in, but he was honest and told you what it was and that you're risking everything.
4. The promoter knew what it was but joined the referral program to lure others in. He did not invest himself, only took profits from the referral program.
5. The promoter was paid to lie about the program and invite people in. He knew what it was, did not invest himself, was being paid a wage.
6. The promoter was an employee of a company that he believed to be legit and paid a wage. He was hired to advertise them and was never told that it's a scam.
If he was a contract worker on a wage you'll be wasting time. In all cases you'll have to prove that he knew what he was promoting, and it would be best if he had a stake in the scheme and pulled out before the collapse. If he also lost money (was scammed), it will make the case much harder if not impossible to win.