The Trinity Mirror group saw £25 million wiped from its market value as its share price dropped from 61 pence on Thursday’s close to 50 pence after 11am on Friday.
It is believed investors fear that the company, which now has a market capitalisation of £128.8 million, will soon have to pay damages over alleged phone hacking.
Trinity Mirror's share price had already fallen more than 12 per cent on Tuesday after news of the civil claims first emerged.
On Friday morning high court judge Mr Justice Vos, who is overseeing the claims against News of the World, announced that he planned to manage the four phone hacking claims filed against Trinity Mirror's newspapers.
Simon Fox, the recently appointed chief executive, said on Wednesday, after news of civil claims first emerged, that the company was launching an investigation into the allegations.
He commented: "Even though we have yet to receive the legal claims which have been reported on, it would be irresponsible of me not to ask our lawyers to look into the four claims that have attracted this recent attention,"
"My clear observations over my first few weeks at Trinity Mirror are that the company operates to the appropriate ethical standards and our editorial procedures and processes are robust. As we have consistently said, all our journalists work within the criminal law and the Press Complaints Commission code of practice."