The mailout encourages recipients to support the charity's safer environment for young runaways campaign, by urging them to lobby their local authority or MP.
The charity's 'Safe and Sound' campaign aims to ensure that food, shelter, protection and hope are available to children living on the streets and those at risk of running away.
It is the first time the charity has integrated a specific campaign theme into a direct-mail pack, which is normally reserved for fundraising purposes only.
The pack includes a leaflet that asks readers to visit a website, where they are asked to become a campaign co-ordinator to collect signatures for a petition and persuade others to provide support.
The campaign began last year after the Government called upon local authorities to provide measures to help young runaways in 2002.
It was backed up by a report, published by the society in March, which carried the first research into the plight of the 15,000 children who are thrown out or forced to leave home each year.
"These are society's disposable children - thrown away or fleeing family violence," said Bob Reitemeier, chief executive of the Children's Society.