Protesters are invited to join a fight to save a service which helps hundreds of vulnerable children every year.
A series of meetings will be held over the future of the St Gabriel's project, which will close its doors in four months.
Teenage mothers and abused children are among those who have been helped by the scheme, which was set up in Brighton more than 25 years ago.
Last week, the project's 18 staff found out they were to lose their jobs when The Children's Society revealed it would pull the funding plug on March 31.
The decision also came as a blow to Brighton and Hove City Council, which was happy to continue funding St Gabriel's.
Campaigners have set up the Friends of St Gabriel's group, which will meet in Brighton next week to decide a plan of action.
A public meeting is planned for January for those who would like to lend their support to the fight.
City councillors, parents and social workers are expected to attend.
Dr Jo Tulloch, who previously worked at St Gabriel's, was horrified to hear of the planned closure and joined the campaign group.
She said: "St Gabriel's is the be all and end all for a lot of people. It is a very special place and the quality of services offered is very high.
"The skills provided are quite unique. Some staff have worked there for 15 years.
"The families getting the services from St Gabriel's will not get these services anywhere else. Once you close a place like this you never reopen it.
"There's a very strong feeling among people to save the service, we just need to mobilise it."
The decision to close St Gabriel's throws the future of the project's £1.5 million building in Wellington Road into uncertainty.
Penny Dene, The Children's Society's director of children and young people, said the decision to close St Gabriel's was part of the charity's decision to re-focus operations nationally.
The project costs £400,000 a year to run, with half the costs being met by the charity.
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