Focus Ireland said the Government is not rolling out enough social housing.
It said only 10% of each of the Land Development Agency's developments will be for these types of homes.
It said every day about three families become homeless - there are now over 1,700 families homeless, including almost 4,000 children.
Focus Ireland spokesperson John O'Hare said funds raised from its Shine A Light Night sleepout tonight aim to help them.
"One of the problems we have is that any discussion about homelessness is reduced to numbers and statistics," he said.
"The reality is that behind every number is a mam, a dad, some children that are suffering and hurting because they're homeless.
"What we hope to do with our Shine A Light campaign is to raise much-needed funds...to get those families out of homelessness and into a home."
