From the New York Times:
Twitter, which began as a side project in a small but failing start-up seven years ago and grew into one of the world’s largest platforms for public conversation, is about to take its biggest step yet into maturity: selling stock to the public.
The company announced on Thursday — in a tweet, one of the 140-character messages that are the backbone of the service — that it had filed paperwork with regulators to eventually sell shares in an initial public offering. However, it had filed the first documents months earlier under a special provision of securities law that allows a company with less than $1 billion in annual revenue to keep its financial data secret until it begins actively marketing its stock to investors.
Twitter’s caution follows the disastrous I.P.O. of its archrival, Facebook. In May 2012, Facebook sold $16 billion in stock to investors, only to see its share price sliced in half in the ensuing months as shareholders worried that the company could not make money from its billion users.