Google's (GOOG) services account for 18% of time spent by U.S. consumers on iOS/Android devices, and Facebook's (FB) services 17%, according to analytics firm Flurry's latest stats. Google's figure includes a 4% share for YouTube. Facebook's doesn't yet account for WhatsApp.
Pressuring Google's usage share: Web browsing activity, to which search activity is tightly linked, accounts for only 14% of all time spent, down from 20% a year earlier. In addition, half that time is claimed by Apple's Safari, which carries steep search traffic acquisition costs for Google.
Google is trying to address the browsing/app issue in part by making its search engine more useful for finding/discovering content within apps. But progress has been gradual.
Nonetheless, as noted by Flurry, eMarketer estimates Google accounted for 49% of 2013 global mobile ad spend, well above Facebook's 17.5%. Contributing factors: Google's mobile search (and search ad) hegemony, a solid mobile display ad position, and Android's dominant position in most international markets.
Flurry thinks Twitter (TWTR) has just a 1.5% usage share. It's worth noting comScore estimates Twitter's app was only used by 22.8% of U.S. smartphone users in January. 77.6% used Facebook's core app, and 27.5% Instagram. Five different Google apps were used by over 40% of users.