San Francisco - Twitter, the microblogging service whose shares have more than doubled since its November initial public offering, will give insiders the first chance to sell their stock tomorrow.

As many as 9.87 million of non-executive employees’ shares will become eligible for sale as agreements that locked them up after the IPO expire, according to filings with the US Securities and Exchange Commission.

That would boost the number of shares available for trading by 12 percent to about 90 million, according to data compiled by Bloomberg.

More stock will start to become available for trading in May.

Twitter has dropped 14 percent since the company’s earnings report last week, which showed slowing growth in signups and declining usage.

While lockup expirations can weigh on a company’s stock, they will eventually bring Twitter to a more justified price given its prospects, said Max Wolff, chief economist and strategist at ZT Wealth in New York.

“Twitter stock was on an unbelievable tear after the IPO, and then hit a wall of worry around the earnings, and now is going to be tested with this lockup expiration,” Wolff said.

“These are all steps on the road to evaluating Twitter not as a great story, but as a publicly traded company with a stock price you have some kind of rational thesis around, and that’s healthy.”

No insiders sold in Twitter’s IPO, meaning none have been able to profit yet from the run-up in the stock price.

Twitter, which debuted November 6 at $26, closed at $56.47 at yesterday’s close in New York.

They touched an intraday record of $74.73 on December 26.

Twitter’s biggest shareholders include co-Founder Evan Williams, who has about a 10 percent stake, and Rizvi Traverse Management LLC, which along with its affiliates held an almost 16 percent stake after the IPO.

Other shareholders include Benchmark Capital, Union Square Ventures, Spark Capital and celebrities such as Ashton Kutcher.

In 2012, Facebook’s shares dropped to record lows amid the rival social network’s larger share-lockup expirations. - Bloomberg News