Groupon is making a fist ton of cash. If they stopped spending money on hiring and marketing, they'd be wildly profitable. Investors have access to all this information.

Also, Groupon has a clear formula for growing and how long it takes that new business to become profitable. That is why they can raise so much investment.

If you can come up with a convincing argument why Groupon is a Ponzi scheme, then call the law enforcement. You'll get on the news for sure!