I'm pretty sure that no one is buying into these Ponzis.  The person running them seems to have a stable of other forum accounts that he uses to claim they are investing and then getting paid back. 

I think if you do the traces on the transactions, you'll see the money is just going in circles.  I did this on one of them just to satisfy my curiosity. 

If you have the ability to do HS math, you should be able to figure out that ponzis don't work.