Joanna Shields, head of social media group Facebook Inc (NASDAQ:FB)’s operations in Europe, is quitting the social media giant to spearhead London’s efforts to compete as a world leader in technology start-ups.

Tech City Investment Organization was set up in April 2011 by the British government to attract foreign investment, focused on an area in London’s east End, dubbed “silicon roundabout” and supporting start-ups looking to expand. Tech City has attracted investments from the likes of Google Inc (NASDAQ:GOOG), Intel Corporation (NASDAQ:INTC), Cisco Systems, Inc. (NASDAQ:CSCO) and other 3,000 companies mainly start-ups. Tech City has received about £4m in public money, and the total could reach nearly £400m, according to plans announced in 2010 by Cameron.

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“The success of Tech City shows just what can happen when we back some of our most innovative and aspiring companies to grow,” Prime Minister David Cameron said in a statement on Sunday.

On Joanna Shields, prime minister David Cameron said “I’m delighted that Joanna is joining the Tech City Investment Organization,” and added “Joanna’s experience will be hugely valuable in supporting Tech City as it goes from strength to strength, and as a business ambassador promoting the UK around the world”.

American-born Shields, before joining Facebook Inc (NASDAQ:FB) in 2010, held senior positions at AOL, social networking start-up Bebo, and Google. Joanna Shields will become chief executive of the Tech City Investment Organization in January, and will also serve as Britain’s business ambassador for the digital industries.

“The seeds have been sown in east London for a dynamic and successful cluster: we have the infrastructure, the technology, and the talent, now we need to accelerate the growth,” Shields said in a statement. “With the right boost now, there is no reason why we can’t make London the number one location for tech in the world”.

“Tech City is a great success story and I believe Joanna Shields has the expertise and ability to make a hugely valuable contribution to its development,” said trade and investment minister Stephen Green, a former chairman of HSBC.

Shields absence will be greatly missed by Facebook Inc (NASDAQ:FB), especially in such turbulent times when the world’s biggest social network is in the process of reassuring shareholders after a rough reception on Wall Street since its high profile listing in May. The company’s declining revenue growth rate has seen its market valuation halve, Facebook Inc (NASDAQ:FB) shares closed at $19.00 on Friday, compared with a $38.00 issue price in May.

“Facebook supports the UK Government’s vision for building a stronger technology-based economy and start-up ecosystem, and we wish Joanna every success,” a company spokesman said.

Zynga Inc (NASDAQ:ZNGA) lost several of its top executives during the previous months, due to concerns of the future of the company. Will the exit of Shields be the beginning for Facebook, as it tries to revive itself after the rough reception on Wall Street?