The family of hostage Norman Kember are appealing for his release in a series of radio and newspaper adverts in Iraq.
Norman Kember has been shown blindfolded and shackled
The appeal to his captors, in Arabic, refers to calls from the Arab and Muslim world for Mr Kember's freedom.
The 74-year-old, from north London, and three other hostages from a peace group remain missing almost two weeks after their captors threatened to kill them.
The Swords of Truth group demanded all Iraqis detained by coalition forces be freed by 10 December - a call not met.
Mr Kember, from Pinner, was seized in Baghdad on 26 November.
He was seized along with Canadians James Loney, 41, and Harmeet Singh Sooden, 32, and an American Tom Fox, 54.
Mr Kember was last seen in a video on 8 December.
The advert gives a phone number for anyone with information to ring
He had travelled to Iraq as a gesture of solidarity with Christian Peacemaker team - a Canadian-based international peace group.
Mr Kember was seen in the last video, aired on al-Jazeera, blindfolded and with his hands tied.
In the joint advertisement, to appear in papers and on radio in Iraq over the new few days, the families call for the safe return of their relatives.
In the advertisement, the families say: "A month has passed since our loved ones - Norman, James, Harmeet and Tom - were kidnapped in Iraq.
"Many clerics and religious figures from the Arab and Muslim world have spoken over the past weeks of the good work they were doing in Iraq and that their organisation have done in Palestine, and they have called for their release.
"We appeal to you to help us ensure the safe return of our relatives.
"If you have any information which can help, please call this number. You do not have to reveal your identity."
TIMELINE OF ABDUCTION
26 November: Norman Kember is reportedly abducted along with three other peace workers
30 November: A video showing the captured peace workers is shown by the previously unknown militant group Swords of Truth Brigade
1 December: Anti-war campaigner Anas Altikriti flies to Iraq to plead for Mr Kember's life
4 December: Mr Kember's wife Patricia makes a plea for her husband
11 December: The original deadline from Mr Kember's captors passes
A telephone number and e-mail address have been set up in the hope the kidnappers will make contact.
Anas Altikriti, of the Muslim Association of Britain, who has been campaigning in the Middle East for Mr Kember's release, said experts in the region suggested the lack of news on his fate was a positive sign.
"If a group, especially an obscure group like this that doesn't really have any kind of track record in this particular arena, if they want to be seen as serious and their demands to be taken seriously, then they would have come out fairly quickly and announced that they had carried out their threat," he said.
Mr Altikriti said it would be a "wonderful gesture" if the men were released before Christmas Day.
The Muslim Association of Britain, meanwhile, renewed its appeal to Mr Kember's captors.
Mr Altikriti told BBC Radio 4 Today's programme: "One of the unique traits of this particular case is the kind of consensus that we have managed to achieve both inside Iraq as well as throughout the Muslim world."
He added that the kidnappers would be aware of this reaction.
The Reverend Alan Betteridge, who is a friend of Mr Kember, said he hoped the group holding the men would respond to the appeal.
"I do hope that at this time of the year as in the Christian world we think of peace and goodwill, that that same idea will come across to all the people involved in this.
"That they will see the message from the family, recognise the genuineness of these people and release them because they are good for the world, the world needs them, we need them."