Steam surpassed its previous concurrent user record on January 7, when it recorded 14.2 million people logged in. That's a significant increase from the 12.3 million that was reported in January 2016. In total, the platform has hundreds of millions of users, though there's no recent data on the exact amount.
Based on player count data, some of the top games on January 7 were Dota 2, Counter-Strike: Global Offensive, and Team Fortress 2. Two of those (Dota 2 and Team Fortress 2) comes from Valve, the company behind Steam.