Twitter interim chief executive Jack Dorsey has bought over 31,000 shares in the social-media firm.

In a show of confidence in the future of the company he co-founded, Dorsey bought 31,627 shares, worth around $875,000 at $27.67 per share.

Dorsey wrote in a tweet, "Investing in @twitter’s future." He became the interim CEO after Costolo stepped down from the position in July.

He now owns about 21.9 million shares, or around 3% of Twitter. He sold over 379,000 shares since November.

In the second quarter 2015 results, Dorsey said growth in audience was not up to scratch even though the company saw good progress in monetisation.

Separately, Twitter director Peter Currie said he had bought about 9,200 shares for $249,000 in stock.

The company’s board member Peter Fenton and chief financial officer Anthony Noto also bought shares last week.

Twitter’s board is considering major change, following news that former chief executive officer Dick Costolo is planning to exit the company.

The company is reportedly looking for a permanent CEO in order to bring more diversity to the board.