FACEBOOK FUELED BY MOBILE: Facebook Inc. worked its way back into the black in the second quarter, with an increase in mobile advertising dollars helping it post a $333 million profit, reversing year-ago losses of $157 million. Revenues weighed in at $1.81 billion and marked a 53 percent increase. Mobile advertising was a key driver in these results, making up 41 percent of the company’s $1.6 billion in ad revenues. In the first quarter, mobile accounted for just 30 percent of ad revenues. Mobile users who logged on at least once per month shot up 51 percent to 819 million in the second quarter. Investors liked the results and pushed Facebook’s stock up 19.6 percent to $31.70 in after-hours trading Wednesday.