With 115.4 million unique visitors in the U.S., Facebook is the number one mobile app by far.
The rest of the ranking, released by comScore, is clearly dominated by Google with five Apps in the Top 10, including rank two (YouTube) and three (Google Play). Ranked at five, we see Pandora Radio with 69 million unique visitors. The ranking closes with Apple Maps and Yahoo Stock, both with an audience of around 42.1 million unique visitors. To see more data about mobile in the States, read ComScore’s "The U.S. Mobile App Report".
This chart shows the top 10 mobile apps by unique visitors.
You will find more statistics at Statista