Twitter Is Still Whistling

Twitter is facing a federal government investigation, competition from Google+ and the departure of two of its founders. But Dick Costolo, Twitter’s chief executive, has a message for the naysayers: the business is growing just fine.

“We’re growing faster than we've ever grown,” Mr. Costolo said Tuesday at the Fortune Brainstorm Tech conference in Aspen. People send a billion Twitter posts every five days and 400 million people visit its Web site – not counting Twitter apps – each month, he said. Still, Twitter is in the early days of turning all that usage into revenue. Advertising on Twitter is growing rapidly, Mr. Costolo said. Last year, Twitter had advertisers in the low hundreds, and that number has increased seven-fold this year.