Twitter (TWTR) failed to add users at a quick enough pace to satisfy investors in the second quarter even as revenue grew sharply. There are questions now about Twitter and whether it can ever become a mass market service like Facebook (FB) and Google (GOOG). On average, Twitter had 316 million monthly active users in the second quarter, up 15 percent year over year, but up less than 3 percent from the first quarter of the year. In fact, monthly average user number grew at its slowest pace since Twitter went public. Twitter's chief financial officer, Anthony Noto, said in a conference call that the company doesn't expect to see 'sustained, meaningful growth'. Noto did not say when that would be, only that it would take a considerable amount of time. Twitter shares have increased roughly two percent since the beginning of the year and have been trading near a 52-week low.