There are 45508 companies listed in stock exchanges around the world. These are listed companies. The number of formal unlisted companies would be a wild guess as there is no central quantified effort to build an international registry.
So taking a different approach, in countries like USA, there is one company for every 11 people. In some others, there are 0. A rough extrapolation based on economic freedom and world wide business numbers from UN reports would mean that there is a company for every 60 people on the planet. That brings us to ~115M companies.