NEW YORK – TWITTER says it plans to join the stock market in the most hotly anticipated flotation since Facebook’s last year.Referring to the official paperwork needed to join the market, the company tweeted: "We’ve confidentially submitted an S-1 to the SEC for a planned initial public offering.”Investors value Twitter, founded in 2006 by Jack Dorsey, Biz Stone and Evan Williams, at more than $10b. Twitter gave no further details as to the timing or price of the offering.Advertisers are keen to target Twitter’s 200 million active users, who send over 500 million tweets a day.