Facebook also continued to show it can weather concerns that it is losing its "cool" factor among teens or irking users worried about privacy. Facebook added another 40 million users in the second quarter, with one-fifth of the world's population now logging into the social network at least once a month. Facebook started placing ads on its mobile site and app only two years ago around the time of its initial public offering. It has now found itself in an entrenched battle with Google, fighting to inhale mobile advertising dollars that would otherwise have gone to the Web, print or television. Anyone else would be a distant third. Facebook is projected to command about 18% of the roughly $17.7 billion U.S. mobile ad market this year, up from 9% two years ago, according to eMarketer. Google will remain No. 1, but its share is expected to fall to 39.8% from 49.8% during that time. Get the full story at The Wall Street Journal and AdvertisingAge Read also "Study: Mobile users who engage with brands use Facebook most" at AdvertisingAge