This cannot be determined. I dont think that the number of people participating in cryptocurrency investments globally will not exceed 100 million. Only about 40 million people may be investing. However, it should increase by several million each year.
It's not only difficult to name up the exact number of people that are using Bitcoin, but another difficult point is what people think a Bitcoin user is. Is it someone that is using Bitcoin once or twice a week, is it someone that is using Bitcoin at least once a month... I think the closest point where we can get an answer to that, is when wallet services, exchanges, gambling sites, etc, bundle their power to share user information with each other to come up with a number.