More than 4,000 potential phone hacking victims have been highlighted by Scotland Yard, detectives leading the investigation said.
Documents handed over by News International contain almost 4,000 names, with hundreds more coming forward to say they had been targeted.
Deputy Assistant Commissioner Sue Akers said officers were seeking to contact all of them "as soon as possible".
She added: "I understand that many people may be upset and will want to seek information from us. I ask them to be patient and reassure them we will contact them if they are affected - have confidence in us to keep our promise but also realise it will take time."
Officers are studying about 11,000 pages of material handed to the Metropolitan Police last month, Ms Akers, who is in charge of Operation Weeting, added.
"I have huge sympathy for those who may have been the victims of phone hacking or intrusion into their private lives," she said.
"It must be incredibly distressing to see details of the information held, or speculation about what may be held, about them in the media. This is forcing them to relive devastating experiences.
"I stand by my commitment that Operation Weeting will contact all those who have some personal contact details found in the documents seized in 2005 and my officers are working hard to ensure it is fulfilled as soon as possible.
"This is taking a significant amount of time and resources. I think it is important that I further explain the scale of the task and the challenges we face."