The appeal comes in response to the region's shortage of carers, which has the largest shortfall outside of London.
Media spokespeople include foster children and a mother whose children are in care.
The misconception that divorcees or childless couples cannot foster will be tackled by the campaign. St Helens marketing officer for adoption and foster care, Joanne Fairclough, said: 'PR is the only way this can be addressed. It can't be done through advertising. It is not easy to conjure up a nice picture of children who need a new mum and dad.'
The 'supermum' image of foster carers who have looked after dozens of children was also a problem, Fairclough said: 'Most people may only foster two or three children. We want more people to do a little.'
Seventy per cent of fostered children eventually return to their birth families, while 30 per cent require care until they are 18.
The campaign will be backed up with media relations and advertising activity in September.
Twenty-one North-West councils are involved, including Knowsley, Cumbria, Bury, Blackburn, Wigan, Warrington, Sefton, Rochdale, Manchester, Liverpool and Lancashire.
- Foster Care Fortnight runs until 22 May.