Analyst ComScore has released its estimates of mobile app usage for 2012 and it appears the Facebook has taken the lead. The Facebook app was the most-used app at the end of 2012, drawing over 85 million unique visitors in December 2012.

Google Maps had steadily led in mobile app usage until only a few months ago. As seen in the graph above, usage of Google Maps dropped considerably in mid-September, when Apple announced it had dropped the app as its official, built-in Maps app. Usage is picking back up, however, now that Google Maps has been released as a standalone app for iOS.

Google won’t worry too much about losing the top spot to Facebook, though. Of ComScore’s top 10 most-used mobile apps in December half are Google apps, including Google Play, Google Search, Gmail, and YouTube. Other highly used apps include Pandora Radio, Apple iTunes, Cooliris, and Yahoo Messenger.

When it come to engagement on mobile, Facebook really has no competition. Of the time spent by mobile users in apps, a full 23% of it was spent on the Facebook app. Instagram comes next with3%, and all of Google’s collective mobile apps only add up to a 10% share of the time spent in apps. Google and Facebook together account for over 1 out of every 3 minutes spent on mobile apps.