Trinity Mirror's share price plunged to a six-week low after its papers were dragged back into the phone hacking scandal with the arrest of four former and serving journalists, as well as reporting tumbling profits in a poor set of financial results for 2012.
Those arrested under the Metropolitan Police's Operation Weeting, its probe into phone hacking allegations, were James Scott, the Sunday People's current editor, Tina Weaver, the former Sunday Mirror's editor, Nick Buckley, deputy Sunday People editor, and Mark Thomas, also a former deputy editor of the paper and who previously worked for the Sunday Mirror.
"We take any allegation against employees very seriously and are co-operating with the police," said a Trinity Mirror spokesman.
Before police announced the arrests, which concern allegations relating to the Sunday Mirror paper from between 2003 and 2004, Trinity Mirror said its pre-tax profit fell by 75 percent in 2012.
The publisher of the Daily Mirror, Sunday Mirror and Sunday People reported a pre-tax profit of £18.9m ($28.2m, €21.8m) in 2012, compared to £74.4m in 2011.
Its Sunday papers have faced fierce competition from Rupert Murdoch's Sunday Sun, which replaced the now defunct News of the World back in April.
Trinity's profit drop was also down to a non-cash goodwill writedown of £60m after the media firm reviewed its digital classified recruitment and property businesses.
It also said it had suffered a "slow start" to 2013, with revenues down as much as 13 percent in the first two months of the year.
Trinity Mirror shares had dropped 16.01 percent on the day in London, hitting 101.00 pence at 14:31 GMT.