There is a stat on Wikipedia:
https://en.wikipedia.org/wiki/Steemit#Steemit_Statistics
Sadly only three rows for the last four month.
And yes registered users where doubled to 800'000. But registered users aren't all that important. What counts is active user. And that dropped last month. (But same for Minds.com — its a close race)
Mind you: I am still an active user who posts here. But i have seen other making a few postings abandon there account again. And the user who introduced me to Steemit is powering down her tiny 30 steem power. Her account is about a year old.