Many of the 5,000 missing refugee and migrant children in German will have been forced into prostitution or harvested for their organs, according to the leader of the country's Muslim council.

Aiman Mazyek, the chairman of the Central Council of German Muslims, said that immediate changes need to be made to the asylum system to protect children and young people.

He demanded to know why Europeans were not speaking out in defence of the missing children.

Vulnerable: Germany admitted that it can't account for some 5,000 refugee children who have vanished since entering the country, since the start of the refugee crisis

'We must assume that many of these children and young people have fallen into criminal circles, that they are forced into prostitution or their organs were removed,' said Mr Mazyek at a press conference, reported Die Welt.

'Where is the outcry? This silence in the face of many missing people can be heard very loudly.'

Germany admitted last week that it can’t account for some 5,000 refugee children who have disappeared since entering the country.

A spokesperson for the Federal Criminal Police (BKA) said that, as of January 1, exactly 4,749 unaccompanied child and adolescent refugees are believed to be missing.

Of them, 431 were less than 13 years old, 4,287 were aged between 14 and 17, and 31 of them were aged 18.

We must assume that many of these children and young people have fallen into criminal circles, that they are forced into prostitution or their organs were removed. Aiman Mazyek, the chairman of the Central Council of German Muslims

That figure is up from 1,637 missing children on July 1 last year.

A spokesperson was not able to rule out the possibility that the vulnerable children had fallen victim to criminal gangs.

Europol, the European police agency, had previously said that at least 10,000 unaccompanied refugee children had gone missing in Europe in the past 24 months.

‘This does not mean that something happened to all of them,’ a Europol spokesman said.

‘Some of the children could actually now be with relatives. But it means that these children are at least potentially at risk.’

Mr Mazyek was joined at the press conference on Thursday by German federal government adviser John Wilhelm Roerig, a leading campaigner against the sexual abuse of refugee children.

Mr Roerig highlighted the risk to refugee children who are staying in asylum shelters.

Lost: Of the missing children, 431 were younger than 13 years old, 4,287 were aged between 14 and 17, and 31 of them were aged 18. Pictured, refugees with children walk towards the Macedonia-Serbia border in February

Innocent: The German federal government adviser John Wilhelm Roerig warned that unaccompanied children living in asylum shelters are also vulnerable to helpers and guards. Pictured, children at the Tempelhof Airport

'I have to warn you, many alleged helpers and guards have too easy access to the children and are able to create a closeness that can be exploited,' he told reporters.

'The refugee crisis is also a crisis of refugee children. They have often experienced terrible things and are especially needy and vulnerable.'

Mr Roerig listed a number of changes that he believes the German government should make in order to better protect children.

These included separate bathrooms for women and children; and ideally separate asylum centres entirely - a system which has already been implemented in some areas of the country.

An increasing number of women and children are leaving mixed housing as a result of a spike in physical and sexual assaults, he said.

The Central Council of Muslims, working with Mr Roerig, is set to release a brochure in German, Turkish and Arabic to educate children on what constitutes abuse, so they know when to report it.