There's no way to figure out how many Bitcoins are still in circulation and how many are lost or stuck on an address that are non accessible anymore. In this article https://www.ccn.com/6-million-bitcoin-is-lost-or-stolen-should-the-real-value-of-btc-higher it says that there are 4 million lost and 2 million stolen Bitcoins but I doubt that this is accurate because there's no possible way to to accurately know the amount of Bitcoins that are stuck forever, and not all lost and stolen Bitcoin are being reported on news or being featured on articles. Also we cannot conclude that Bitcoins are lost if it hasn't been moved from an address to another for a very long time.