NEW YORK (REUTERS) - Billionaire Elon Musk was sued on Tuesday (April 12) by former Twitter shareholders who claim they missed out on the recent run-up in its stock price because he waited too long to disclose a 9.2 per cent stake in the social media company.

In a proposed class action filed in Manhattan federal court, the shareholders said Mr Musk, the chief executive of electric car company Tesla, made "materially false and misleading statements and omissions" by failing to reveal he had invested in Twitter by March 24 as required under federal law.

Twitter shares rose 27 per cent on April 4, to US$49.97 from US$39.31, after Mr Musk disclosed his stake, which investors viewed as a vote of confidence from the world's richest person in Twitter.

Former shareholders led by Mr Marc Rasella said the delayed disclosure let Mr Musk buy more Twitter shares at lower prices, while defrauding them into selling at "artificially deflated" prices.

The lawsuit seeks unspecified compensatory and punitive damages.

A lawyer for Mr Musk had no immediate comment. Tesla is not a defendant.

Mr Rasella said he sold 35 Twitter shares for US$1,373, or an average price of US$39.23, between March 25 and 29.

US securities law requires investors to disclose within 10 days when they have acquired 5 per cent of a company, which in Mr Musk's case would have been March 24.

Twitter announced on April 5 that Mr Musk would join its board of directors, but this week said he had decided not to.

By not joining the board, Mr Musk, a prolific Twitter user, can keep buying shares without being bound by his agreement with the company to limit his stake to 14.9 per cent.

Some analysts have suggested Mr Musk could push Twitter to make changes, or even pursue an unsolicited bid for the company.

Mr Musk is worth US$265.1 billion (S$361.7 billion), according to Forbes magazine.