Twitter announced on Thursday that it is going public in a format that was perfectly apt for the microblogging service: it sent out a tweet to its close to 24 million followers around 5 p.m. ET announcing the most hotly anticipated initial public offering since Facebook's IPO. 

"We've confidentially submitted an S-1 to the SEC for a planned IPO," the tweet said. "This tweet does not constitute an offer of any securities for sale."

An S-1 form is a financial document that U.S. companies file with the Securities and Exchange Commission in New York as part of the formal IPO process.

Under legislation passed last year called the Jumpstart Our Business Startups, or JOBS Act, U.S. companies with revenue of less than $1 billion US a year can file a secret IPO and need not make the filing public until 21 days before what is known as the "road show" portion of the IPO process, which the company uses to drum up interest in its stock among investors and fund managers.

Facebook a cautionary example

Analysts who had been watching the San Francisco-based company ramp up its efforts to boost advertising revenue had been expecting the IPO to be filed some time in October or November.

Twitter's growth

Founded in 2006 and named after a sound tiny birds make, Twitter has since grown into a communications medium of remarkable cultural significance despite its relatively small size. In seven years, Twitter has grown from a few thousand users to more than 200 million. Its users include heads of state, celebrities, activists, journalists and ordinary folks of all ages.

The Associated Press

They will be closely watching Twitter to see if it avoids the pitfalls that plagued Facebook's bungled IPO in May 2012, which many saw as ill-timed. Facebook initially priced its stock at $38 a share but saw its share price plunge after computer glitches on the Nasdaq delayed trading. Its stock price only recovered its value this past July when it traded above $38 for the first time since the IPO.

Most of Twitter's revenue comes from advertising. Research firm eMarketer estimates that Twitter will generate $582.8 million in worldwide ad revenue this year, up from $288.3 million in 2012.

By comparison, Facebook had ad revenue of $1.6 billion in the April-June quarter of this year. By 2015, Twitter's annual ad revenue is expected to hit $1.33 billion.

With files from The Associated Press