In 2014 Riot released numbers of 7.5MM peak concurrent players for League of Legends (off a MAU 67MM) and in 2016 reported a MAU of 100MM (but no new concurrency figures). Those are old stats but still useful for comparison.
Disclaimer: I work at Riot but don't have any internal numbers to share.
arkem|6 years ago
https://na.leagueoflegends.com/en/news/game-updates/special-...