Mark Zuckerberg's net worth has plunged about $5 billion after Facebook shares slumped following the Cambridge Analytica scandal in which data of 50 million users was reportedly misused.

The company's stock plummeted nearly 7 percent on Monday putting Facebook on track for their worst day in four years.

Zuckerberg, who is currently the seventh richest person in the world, holds roughly 400 million shares, or 16 percent, in Facebook.

Following the drop, Zuckerberg is now worth an estimated $69.5 billion, according to Forbes.

His company is facing mounting calls to testify after reports emerged that the firm, which has links to President Donald Trump's campaign, gained inappropriate access to data on 50 million Facebook users.

The reports have prompted a review by the company and expressions of concern by several US lawmakers who are demanding that Zuckerberg be grilled by the Senate Judiciary Committee.

Facebook shares slumped 5.3 percent on Monday as several US lawmakers demanded that Mark Zuckerberg be grilled over the Cambridge Analytica data scandal

The company's stock plummeted nearly 7 percent on Monday putting Facebook on track for their worst day in four years

Pictured above is the drop in shares from early Monday morning

One Wall Street analyst said the reports raised 'systemic problems' with Facebook's business model and a number said it could spur far deeper regulatory scrutiny of the platform.

'We think this episode is another indication of systemic problems at Facebook,' said Brian Wieser, analyst at New York-based brokerage Pivotal Research Group, which already has a 'sell' rating on a stock that rose 60 percent last year.

Wieser argued that regulatory risks for the company would intensify and enhanced use of data in advertising would be at greater risk than before.

He added, however, that it was unlikely to have a meaningful impact on the company's business for now, with advertisers unlikely to 'suddenly change the trajectory of their spending growth on the platform'.

The losses in shares on Monday would be among Facebook's biggest daily fall, including a broader market pullback in February. In January, when Facebook announced changes to its newsfeed, which it said would hit user engagement in the near term, shares fell 4.5 percent in one day.

Facebook announced on Monday that it had hired a digital forensics firm to investigate the handling of data leaked to a consulting firm.

A statement said the forensics firm Stroz Friedberg would 'conduct a comprehensive audit of Cambridge Analytica,' and that the company had agreed to comply and provide access to its servers and systems.

Facebook said University of Cambridge psychologist Aleksandr Kogan, who developed the app used to harvest user data, also agreed to cooperate.

It added that Christopher Wylie, the Canadian data analytics expert who worked with Kogan and who revealed the data leak to media, had declined to cooperate with the audit.

Senator Mark Warner and Senator Amy Klobuchar are among those demanding that Zuckerberg be grilled by the Senate Judiciary Committee

'I've called for more transparency & accountability for online political ads. They say 'trust us.' Mark Zuckerberg needs to testify before Senate Judiciary,' Klobuchar tweeted

Facebook suspended the access of Christopher Wylie, a former Cambridge Analytics employee who has emerged as a primary source

Facebook has been facing new calls for regulation from US Congress and questions about personal data safeguards after the reports from the New York Times and London's Observer over the weekend regarding the Cambridge Analytica scandal.

The papers reported on Saturday that private information from more than 50 million Facebook users improperly ended up in the hands of data analytics firm Cambridge Analytica, and that the information had not been deleted despite Facebook demands dating back to 2015.

Sen Amy Klobuchar tweeted on Saturday: 'This is a major breach that must be investigated. It's clear these platforms can't police themselves.

'I've called for more transparency & accountability for online political ads. They say 'trust us.' Mark Zuckerberg needs to testify before Senate Judiciary.'

US Sen Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee, echoed Klobuchar's complaint.

'This is more evidence that the online political advertising market is essentially the Wild West,' he said. 'It's clear that, left unregulated, this market will continue to be prone to deception and lacking in transparency.'

Massachusetts Attorney General Maura Healey said on Twitter that 'Massachusetts residents deserve answers' and announced that her office will investigate.

Cambridge Analytica is best known for working on Trump's 2016 campaign.

Reports stated that senior members of Cambridge Analytica met with Russian business executives ahead of the 2016 campaign.

Facebook suspended the group on Friday for not fully deleting all of the data it had obtained.

It also suspended the access of Kogan, the academic who created the app in question; and Wylie of Eunoia Technologies, who also allegedly received user data from the app.

Wylie is a former Cambridge Analytics employee.

A British lawmaker accused Facebook on Sunday of misleading officials by downplaying the risk of users' data being shared without their consent.

Conservative legislator Damian Collins, who heads the British Parliament's media committee, said he would ask Zuckerberg or another Facebook executive to appear before his panel, which is investigating disinformation and 'fake news'.

Collins said Facebook has 'consistently understated' the risk of data leaks and gave misleading answers to the committee.

It follows reports that Cambridge Analytica, which is best known for working on Trump's 2016 campaign, had improperly obtained Facebook user data and retained it after claiming it had deleted the information

'Someone has to take responsibility for this,' he said. 'It's time for Mark Zuckerberg to stop hiding behind his Facebook page.'

FACEBOOK TO HIRE DIGITAL FORENSIC FIRM: We have hired a digital forensics firm, Stroz Friedberg, to conduct a comprehensive audit of Cambridge Analytica. Cambridge Analytica has agreed to comply and afford the firm complete access to their servers and systems. We have approached the other parties involved - Christopher Wylie and Aleksandr Kogan - and asked them to submit to an audit as well. Mr Kogan has given his verbal agreement to do so. Mr Wylie thus far has declined. This is part of a comprehensive internal and external review that we are conducting to determine the accuracy of the claims that the Facebook data in question still exists. This is data Cambridge Analytica, SCL, Mr Wylie and Mr Kogan certified to Facebook had been destroyed. If this data still exists, it would be a grave violation of Facebook's policies and an unacceptable violation of trust and the commitments these groups made. We are moving aggressively to determine the accuracy of these claims. We remain committed to vigorously enforcing our policies to protect people's information. We also want to be clear that today when developers create apps that ask for certain information from people, we conduct a robust review to identify potential policy violations and to assess whether the app has a legitimate use for the data. We actually reject a significant number of apps through this process. Kogan's app would not be permitted access to detailed friends' data today. Advertisement

Collins also accused the head of the UK-based data firm Cambridge Analytica, Alexander Nix, of lying.

Nix told the committee last month that his firm had not received data from a researcher accused of obtaining millions of Facebook users' personal information.

Former Cambridge Analytica employee Chris Wylie said that the company obtained information from 50 million Facebook users, using it to build psychological profiles so voters could be targeted with ads and stories.

Wylie told Britain's Channel 4 news that the company was able to amass a huge database very quickly from an app developed by an academic that vacuumed up data from Facebook users who agreed to fill out a survey, as well as their friends and contacts - a process of which most were unaware.

'Imagine I go and ask you: I say, 'Hey, if I give you a dollar, two dollars, could you fill up this survey for me, just do it on this app', and you say, 'Fine,'' he said.

'I don't just capture what your responses are, I capture all of the information about you from Facebook. But also this app then crawls through your social network and captures all of that data also.'

Wylie said that allowed the company to get roughly '50 million plus' Facebook records in several months. He also criticized Facebook for facilitating the process.

'Why Facebook didn't make more inquiries when they started seeing that, you know, tens of millions of records were being pulled this way, I don't know,' he said.

Lawmaker Collins said he would summon Nix to reappear before the Parliament committee.

'It seems clear that he has deliberately misled the committee and Parliament by giving false statements,' Collins said.