Facebook will have to do a lot of work to build its revenue and sustain its US$74 billion ($92 billion) market value, says the company's former marketing director and sister of co-founder Mark Zuckerberg.

Randi Zuckerberg was a presenter at a social media event in Auckland yesterday but spoke to the Herald about her brother's website, which has more than 900 million users worldwide.

While some social networks will "come and go", Zuckerberg said Facebook had lasting appeal.

"I do think that things like sharing photos, connecting with people you've lost touch with, they are human behaviours and something that's always going to happen ... I think [Facebook] tapped into a human need and emotion to connect with people," she said.


While there has been scepticism around Facebook's market value since it floated in May, Zuckerberg said the company would be able to generate the revenue to sustain its worth.

"It's going to take a lot of work, getting into regions like China, into regions like India and Brazil," she said.

"I do think it's accurate to imagine a world where half the people on the internet are on Facebook, or more." As well as pushing more into growing economies, Facebook also needs to focus on its service for mobile users, the 30-year-old entrepreneur said.

While half of all Facebook users are now accessing the social network on mobile devices such as smartphones or tablet computers, this platform does not have the same level of advertising, and therefore revenue, as the core website.

"Fifty per cent of people who log on to Facebook now are doing it from their mobile and you just can't afford as a business to lose all that revenue," she said.

Although she left the company last year, Zuckerberg still has a stake in the firm, which was valued at US$104 billion at its initial public offering in May. Its value has since slipped and its market capitalisation was around US$74.2 billion yesterday.

Zuckerberg believed Facebook will experience the same growth pains as tech giants like Microsoft or Google.

"They started doing one thing really well and you see now that Google tries to do everything. They want to do maps and email and they want their own social network," she said.

"When you try to do everything well you end up doing nothing well. "I think Facebook is going to have a lot of the same problems, as they're growing they want to be everything to everyone."

Zuckerberg has now founded her own firm, RtoZ Studios, which she says will look to build and invest in televisions shows that use social media in interesting ways.

While she praised the "incredible things" her brother achieved in founding Facebook, Zuckerberg said she doesn't envy the "notoriety" he has gained.

"[Mark's] done incredible things, he also can't walk down the street without people seeing him and recognising him," she said.

"I value my personal privacy a lot, especially having a little baby and a family.

"I don't think I would ever want that notoriety. That's why I don't think there is any sort of sibling rivalry."