Who Uses Esperanto?
When people ask this question what are they really trying to find out? How many people speak the language? Is there a country which speaks it?
Clearly they don't want a list of the names of all the people who use Esperanto because that wouldn't tell them very much. Or are they looking for some big names to see how much credibility Esperanto has? They certainly exist: you may recognise some names this list.
The real question would be to ask where Esperanto is used large scale on a regular basis to facility cooperation and collaboration across language barriers. Unfortunately, because of huge obstacles which Esperanto faces of national interest, inertia, and downright hostility, the answer to that question is "very little" ... other than, of course, the army of enthusiasts who have, voluntarily in their own time, learned the language and use it daily whenever they can.
So that's the answer to the question. At this moment in time the tower of Babel has proved very resistant to its cure. My own opinion is that we need another method of delivering the drug. We need to convince international bodies, whether charities or companies, that by training their workers in Esperanto they will make huge savings both in time and in money by avoiding translation and interpretation costs. There are already signs that this is taking place.