According to an unsubstantiated report at Bloomberg, Fortnite player numbers are up 60% since June. The article claims that player numbers sit at about 200M, up from the last official player count of 125M in June and "almost equal to the population of Brazil". The caveat in all this, of course, is that Bloomberg does not provide a source for these numbers and there doesn't appear to be any information released from Epic itself.
While no source is reported, the thought of 200M Fortnite players may not be all that far-fetched. The game has been setting record after record since its launch in late 2017 including 8M concurrent users. More recently, Epic raised $1.25B from an investor group that brings the company's value to $15B.
We'll be reaching out to Epic to see if we can dig up confirmation of the numbers.