Pictured: Mark Zuckerberg and Priscilla Chan look miserable on their honeymoon in Rome (maybe they are thinking about his lost billions in botched Facebook IPO)

With their long faces and blank expressions, Mark Zuckerberg and Priscilla Chan do not look like a couple enjoying their honeymoon in the Eternal City of Rome.

Settling down for a meal surrounded by other diners in the heart of the Italian capital, the Facebook CEO seems to be staring straight past his new bride while she looks right past the multi-billionaire and at the floor.

Maybe the couple are preoccupied with the disastrous floatation of Facebook onto the stock market which has seen the social networking giant lose billions of dollars off its initial listing price.

Why the long faces?: Mark Zuckerberg and Priscilla Chan look awkward as they eat on their honeymoon in Rome

Honeymooning in the Italian capital, Zuckerberg and Chan have been spotted around Rome by keen eyed locals and their movements have been posted not onto Facebook, but on Twitter.
So far the couple have taken in The Vatican's Sistine Chapel, the Spanish Steps and eaten at Pierluigi restaurant which has been an institution in Rome since 1938.

 

Tying the knot last weekend in the backyard of their $7 million home in Palo Alto, California in front of 100 guests, the wedding came one day after Facebook went public and was valued at $100 billion
During the ceremony, the couple of nine years apparently 'couldn't stop grinning' throughout and even went as far as to write their own vows.

Priscilla Chan seems to look past new husband Mark Zuckerberg as they eat their meal on honeymoon in Rome

The Colosseum in Rome is one of the sights that Priscilla Chan and Mark Zuckerberg have visited

The Papal Basilica of Saint Peterislocated within the Vatican City has also been visited by the honeymooning couple

Walking down the aisle wearing a $4,700 gown designed by Los Angeles-based designer Claire Pettibone, Chan was accompanied by the couple's Hungarian sheepdog, Beast.

The ceremony was a surprise to the 100 or so guests who gathered in the backyard of the Palo Alto home of Zuckerberg and the Facebook CEO is rumoured to have told his wife-to-be's grandmother of the intended nuptials by speaking to her in Chinese.

Inspired to learn the language by his new wife, Zuckerberg had been learning Chinese for two years.

Guests at the wedding enjoyed simple food from the newly wed's favourite Palo Alto Mexican and Japanese restaurants, Palo Alto Sol and Fuki Sushi, with the Mexican entrees reportedly costing $7.50 for each person.

True love: Priscilla Chan, the new Mrs Mark Zuckerberg, was walked down the aisle two Saturday's ago by the couple's dog Beast, a Hungarian sheepdog. The couple also wrote their own vows

It is thought that Zuckerberg and Chan had been planning the surprise wedding for over seven months, but had not even revealed that they were engaged.

Guests had arrived believing that they were there to celebrate Chan's graduation from her degree in pedatrics.

However, they were greeted with the sight of the multi-billionaire wearing a suit and tie, instead of his more usual jeans and hoodie.

Entertainment was provided by Green Day lead singer Billie Joe Armstrong and he played 'Last Night on Earth' as the couple performed the first dance.

Married: The couple have been together for nine years, but did not reveal their engagement

However, despite being on honeymoon and incognito for the past week, Zuckerberg has had a massive reversal in fortune since his wedding just over a week ago.

The much vaunted IPO has run into severe difficulties, with the share price down from $38 to $31 amid acrimony and accusations that the company was overvalued before the launch.

The Facebook founder is being sued in a class action for $2.8 billion for allegedly deceiving shareholders over the disappointing stock market flotation.

Couple: Ms Chan and Mr Zuckerberg met when they studied at Harvard and have been together ever since

He has also been accused of warning big investors of worsening revenue forecasts ahead for the social networking giant but not informing the public.

The lawsuit was filed in New York against Zuckerberg and senior Facebook executives by US law firm Robbins Geller, which in 2008 won a £4.5billion settlement for the shareholders of Enron.

The class action alleges that Facebook 'selectively disclosed' concerns that the company was struggling to raise money from users who access the social networking site via smartphones rather than PC's.

Guests: Those invited thought they were attending a party to celebrate Ms Chan's graduation

Arrival: Guests were pictured turning up at the Palo Alto home on Saturday afternoon

Private: Mr Zuckerberg is known to be secretive about his personal life despite running a social network

The lawsuit filed last week in the US District Court in Manhattan states that the Facebook as well as investment banks Goldman Sachs, JP Morgan and Barclays Capital secretly let 'certain preferred investors' know there were concerns over the share issue, thereby enabling them to sell quickly.

'The true facts at the time of the IPO were that Facebook was then experiencing a severe and pronounced reduction in revenue growth due to an increase of users of its Facebook app or website through mobile devices rather than a traditional PC such that the company told the underwriter defendants to materially lower their revenue forecasts for 2012.' states the lawsuit.

The lawsuit seeks to claim the money lost from the current drop on the opening price of $38.

Drinks: The Facebook founder ordered large amounts of alcohol in anticipation of the party

'We are seeking damages to the value of the amount investors have lost, which is $7 per share for 421million shares,' said David Rosenfeld, a partner at Robbins Geller, the law-firm who has been charged with handling the class action.

'Mr Zuckerberg was put on the lawsuit because he was one of those who signed the stock market registration statement, which makes him liable for anything which is not true on it.'

Flotation: Mr Zuckerberg opened trading on the Nasdaq last Friday, the day of Facebook's IPO

Indeed, anger has also been personally vented towards Zuckerberg as it was revealed he sold 30.2 million of his own shares very soon after the launch, making himself $1.13 billion.

In a statement, Morgan Stanley said that it 'followed the same procedures for the Facebook offering that it follows for all IPOs. These procedures are in compliance with all applicable regulations'.

Facebook spokesman Andrew Noyes said: 'We believe the lawsuit is without merit and will defend ourselves vigorously.'