Along with the growing adoption of smartphones, app usage is increasing as well.
Follow up:According to Flurry Analytics, overall app use increased 115 percent in 2013, with the fastest growing app categories being messaging & social and utilities & productivity. Flurry reports app use in terms of app sessions rather than in terms time spent with apps, i.e. people have opened gaming apps 66 percent more often in 2013 than in 2012.
You will find more statistics at Statista