PALO ALTO, California (Reuters) - Facebook plans to expand and simplify its mobile platform for the 200 million users who access the world's largest social network from their cellphones, but denied persistent rumours it was developing its own phone.

CEO Mark Zuckerberg said yesterday the social network, which has tripled its mobile users from just 65 million at the same time last year, will also make its "Facebook Places" physical location-based feature available on Google Android-based smartphones.

As an example of the new features it will build into the mobile version, it will help local merchants offer ad-hoc deals to customers who "check in" nearby, revealing their physical location.

The company is stepping up efforts to make its 500-million-member social networking service available to consumers when they are away from their PCs.

Facebook is one of several established web companies, including Google and Yahoo, seeking to expand their businesses to mobile devices as consumers increasingly surf the web and send emails on Internet-connected mobile phones.

Its mobile users are twice as active on Facebook as people who access the service on their personal computers.