It is difficult to know the number of the original users of the bitcoin. We all know that the weakness of the system is anonymous data collected could not be accurate. Perhaps we can only estimate that the number of users without being able to ascertain the truth.
That's right. The actual number of bitcoin users cannot be counted, cause of it's increasing every day. Bitcoin is spreading over the world and the last counted number was 2.5 millions, but I am sure that the current number is much higher.