Of course, when the project has an announcement thread you can report it to DT members and they will tag this project as a probable scam.
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Legal action or just want to warn everyone the project it's a scam, for legal action i think depending on the law country and residence country the scammer live. If you just want to give some warning the project its a scam, you can go to the "Scam Assumption" board and make a thread about the scam project.
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I think this is not what OP need. These suggestions are only for this forum, which really got limitation.
I think what OP needs is some government authorities or any accredited by government that will govern the cryptocurrency, just like what @CuriousGeorge, which is the SEC.
Yes, we can report some of these on SEC, but most of the time SEC got no any chance to take down this kind of fraud especially in our country which all they can do is publish some advisories and notices for some fraud related activities especially using cryptocurrencies.
The OP should be willing to spend his own resources if he is willing to push thru the filing of fraudulent project.
Because the reason why there are failed complaints, because most of these complainants gave up because of lack of resources and financial support.
Reporting is quite easy but going beyond legal proceedings will take a lot of your resources.
Now, if you have no resources in the first place, just report the site to google as scam site or here in the forum, to avoid additional victims.