The Fostering Network says four extra carers are recruited a week to keep up with demand.
There are currently some 2,000 children in foster homes, a figure which has increased 5% in the last year and 8% in the past decade.
Some of the difficulties include fewer homes and replacing those who have retired.
Margaret Kelly from The Fostering Network said: "In short, we urgently need local adults and families to provide loving and supportive homes for some of our most vulnerable children and young people."
The stark truth is that many of these children and young people will have experienced real trauma and often not had a positive experience of family life
The Belfast Health and Social Care Trust has the highest number of fostered children at 489.
There are 447 children in care in the Northern area.
Ms Kelly explained that there is no average time frame for a foster care placement. Some children stay with families past the age of 18 or 21 and others return to their parents.
She continued: "Fostering certainly isn't a 'one-size-fits all' scenario - there are many different types of fostering that people choose, according to lengths of time, certain ages, gender and ethnicity, and children with specific specialist needs."
The Regional Adoption and Fostering Service (RAFS) works closely with the five health trusts to recruit, support and provide learning and development opportunities for both foster carers and adoptive families across the region.
RAFS manager Una Carragher said fostering enabled children and young people to experience a stable home life where they could develop and grow.