The popular micro-blogging and social networking service Twitter is not for sale, one of the company's founders said on TV on Wednesday.

Biz Stone made the declaration in an appearance on the ABC show The View.

When host Barbara Walters -- mentioning rumors that Google Inc, Microsoft Corp and Apple Inc might be interested in acquiring the company -- asked whether Twitter is for sale, Stone answered, no.

We're just getting started as I've said. The company is two years old, we have so much to do, so much product stuff to fix, and so much growing to do.

Twitter has been the subject of takeover speculation since the company turned down a $500 million acquisition offer by social networking heavyweight Facebook.

Twitter is a free service that allows people to send short, 140-character text messages to their network of friends. It has become something of a cultural phenomenon, with politicians, celebrities and athletes all signing up to send messages, or tweets, to a growing audience of followers.

According to Nielsen Online, which measures Internet traffic, Twitter's website had more than 7 million unique visitors in February, compared to 475,000 in February 2008.

The company, based in San Francisco, California, is focusing on monetizing its service this year.

(Reporting by Gabriel Madway; editing by Carol Bishopric.)