First of all ...What is an active user?
For Steam an active user is somebody who logged on steam the last 30 days (so you who would say I have three steam accounts but did not go online for years doesn't count)...
Press release:
GDC 2015 will mark the 13th anniversary of Valve's first public announcement of Steam, which has since become the leading platform for PC, Mac, and Linux games and software.
In the last year, Steam added new services and features - including In-Home Streaming, Broadcasting, Music, and user created stores - as it grew to over 125 million active accounts worldwide.
Steam now offers 4500 games, with 400 million pieces of user-generated content contributed by members of the Steam Community.
On january 2014 they passed 75 million.....Last september they hit 100 million...Steam keeps on growing.