Certain aspects of Bitcoin do appear to have certain characteristics of a Ponzi scheme in so far, as early adopters (people on top of the typical Ponzi-pyramid or Ponzi-row) profit most from it, if they decide to hold their coins. But Bitcoin doesn't need new people in order to work or in order to remain functioning.
If you are trying to compare it to a pyramid scheme it most certainly does need new people to work. Without new members in the market to drive the price up there would be nothing for the early adopters to sell. The value would drop to zero quickly and their wouldn't be enough buyers to sell all your coins to. If you think about it, in order for say Satoshi to sell the first million mined coins at just $1,000 it would likely take millions of buyers buying coins at the same time to keep the price stable. If Bitcoin has millions of buyers and users of coins daily then the adoption is large enough that it's not a pyramid scheme but a working economy.