Mark Zuckerberg is dog-tired and perhaps a little grumpy. The 24-year-old founder of Facebook is in London towards the end of a week-long tour of Europe and has been averaging less than five hours' sleep a night.

Being the “face” of Facebook is not his favourite part of the job and he has had some tricky questions to fend off from the European media about Facebook and its future development, particularly the niggling doubt over exactly how and when the social networking site is going to make money.

The technology blogs in Silicon Valley have been giving Facebook a hard time recently. The phenomenal popularity of the site — which is not even five years old — is no longer enough for some analysts.

Mr Zuckerberg and three others launched the site from their Harvard dorm room in early 2004. By the end of the year it already had one million active users — now it has exploded past the 110 million mark and shows no sign of slowing down.

The recent growth spurt has been powered by Facebook-users translating the site into local languages. The Spanish version has swept Latin American countries and Chile is about to become the first country in the world where more than 50 per cent of the online population are active users of the site.

In the UK there are 12.6 million active users — about a third of the online population — and Mr Zuckerberg is in London to talk to developers who are creating applications by the thousands for the Facebook site.

This is a key part of the Facebook strategy — not to try to do everything themselves. The company launched Facebook Platform last year, allowing developers to build features for other users within the site and make money from selling them. This resulted in an avalanche of applications — some annoying, some trivial and some useful — which has helped to make the site a richer experience.

Mr Zuckerberg says: “We realised there was no way we were going to be able to build all the different ways that people would want to share. The web is just expanding so quickly — we found that a good strategy has been to focus on one or two things that we can do really well.

“For us that's helping people connect with people and things that they care about. You are better off focusing on those things and helping to build an eco-system around you for all the other stuff. No one can do everything.”

In May, Facebook went further and allowed third-party websites to take the basic tools of Facebook and build it into their pages. While this “open platform” strategy is hardly ground-breaking — Google, Microsoft and Apple do the same thing — Facebook has used it to improve its appeal to become the fourth-most-visited website on the planet while retaining a comparatively small workforce of about 700 employees.

And, unlike those big beasts, Facebook is still independent, still private, still, in fact, very much Mr Zuckerberg's baby — and that is the way he wants it to stay while he concentrates on growing the user base.

“People all over the world have friends, family, co-workers they want to stay connected to and we have found that Facebook is something everyone could use. We have just hit this big milestone — 100 million active users — and in a lot of ways that is a really cool thing for us, but in a lot of ways it is really just the start.”

Some have mistaken his ambition for hubris. Mr Zuckerberg's geeky, aloof style can be awkward but there is no doubting the drive of a man who happily admits that the only thing he does outside work is sleep.

What about making money? Turning that huge growth into cash is proving problematic. By Mr Zuckerberg's own estimates in early 2008 Facebook will make only about $300 milllion (£173.5million) in revenues this year, mainly in display advertising on the site in a deal with Microsoft, and will have a negative cashflow of about $150 million. Yet Mr Zuckerberg says that he is in no hurry. For the time being, he simply wants enough income to “sustain ourselves”. This attitude, especially in gloomy economic times with the prospect of an IPO disappearing over the horizon, has attracted criticism.

Mr Zuckerberg says that Facebook has a strong advertising business and it is building an international salesforce to improve it further. It is also experimenting with a new type of advertising product - “engagement ads” which encourage users to share and comment, raising brand awareness. MTV recently had a successful trial with a promotion for its video awards on the site.

Yet the truth is that making money is not Mr Zuckerberg's prime motivation (he is angrily forceful on this point). He retains his youthful idealism that Facebook can and should change the way people live for the better by connecting them to each other. “The goal of the company is to help people to share more in order to make the world more open and to help promote understanding between people. The long-term belief is that if we can succeed in this mission then we also be able to build a pretty good business and everyone can be financially rewarded.”

In the meantime, in an effort to keep senior staff happy after a flurry of departures, including Dustin Moskovitz, the co-founder, Facebook is to help employees to sell their company shares privately, up to a value of $900,000 each. The private stock sales are said to be at a valuation of only $3.75 billion, a huge drop from the $15 billion valuation of a year ago when Microsoft took a 1.6 per cent stake for $246 million.

For the moment such statistics do not overly concern Facebook's chief executive. He believes that building the business is the key to success. He has been pretty good at it so far.

Q&A

If you could change one thing in the financial and commercial environment, what would it be?

There is so much going wrong in the current financial climate... pass.

Who is or was your mentor?

Donald Graham, chief executive officer and chairman of the board of The Washington Post. He takes a very long-term view on business. So much of technology is focused on a really short cycle.

Does money motivate you?

No.

What is the most important event of your working life?

The launch of Facebook in 2004.

What gadget must you have?

A Blackberry and an iPhone.

What does leadership mean to you?

Leadership is basically about creating focus. It is about ensuring we are focused on the right stuff and getting good people in to help build what we are trying to do.

How do you relax?

I sleep.

CV

Born: May 14, 1984 in Dobbs Ferry, New York

Education: Attended state schools and then sent to the exclusive Phillips Exeter Academy, New Hampshire (2000-2002); Studied psychology and computer science at Harvard University but dropped out.

Career: Launched Facebook with Dustin Moskovitz, Chris Hughes and Eduardo Saverin from their Harvard dorm room in February 2004. By March, it has expanded to Stanford, Columbia and Yale. In June 2004 the base of operations was moved to Palo Alto, California.

Job description: CEO of Facebook, responsible for setting the overall direction and product strategy for the company. He leads the design of Facebook's service and development of its core technology and infrastructure.

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