Natalie Bracht suffers from a personality disorder
A woman fled her Wearside home with her five daughters when she found out they were being taken into care.
Natalie Bracht, 34, left her Sunderland home on 17 May with her children and is believed to have travelled to London.
Police said they are concerned for the safety of the girls, aged between five and 13, because Ms Bracht has a personality disorder.
Northumbria Police officers are being assisted by their counterparts in the Metropolitan Police force.
After recent information placed the family in the Harlesden area of London, officers now believe she may have moved to another part of the city, or even returned to the North East.
On Monday Northumbria Police were granted permission by the High Court in London to reveal that the children are the subject of interim care orders.
Det Sgt Dave Willett said: "We went to the High Court because we felt that it would help our search for the girls and their mother if the public knew they should be in the care of their local authority.
"Natalie has been previously assessed as having a histrionic personality disorder.
"She and the girls have no visible means of support and I would urge anyone who may be sheltering or supporting them financially to consider her mental condition and the care orders.
"We have real fears for the welfare and safety of the girls and our number one priority in this case is to get them home safe and well."
Symptoms of Ms Bracht's disorder can include a tendency to make rash decisions and show exaggerated displays of emotion.
Sufferers often need to be the centre of attention and have been known to self-harm.
Ms Bracht moved to the North East from Germany in 2006 with her children and speaks good English, with a strong German accent.
The father of three of the girls has travelled to the UK from Germany to help with the investigation.