The Strictly Come Dancing 2012 finalist has thrown her support behind Foster Care Fortnight, which launched on Monday and lasts until May 26.
Before her dancing exploits, Ms Harmer, from Easthampstead, was best known for playing the role of Tracy Beaker - the star of the TV adaptation of Jacqueline Wilson's book.
She said: "I grew up playing a girl who lived in a children's home and then with a foster carer, and I have met many children with similar experiences.
"I have seen the positive affects that living with foster carers, who have the right skills, commitment and big hearts, can have on children.
"I hope you consider putting yourself in the frame and becoming a foster carer so you can help give one of the real-life Tracy Beakers the stability, love and support that they long for."
Bracknell Forest Council is joining all other Berkshire unitary authorities - including the Royal Borough and Wokingham Borough Council - to raise awareness for the need for more foster carers.
Janette Karklins, director of children, young people and learning at Bracknell Forest Council, said: "Foster families are an essential part of the care we provide for some of our children.
"Being a foster carer is very special and we always need more people to come forward and take on this important role.
"Foster carers come from a wide variety of backgrounds and experiences, they may or may not have children of their own, all we ask is that they have the ability to care for a child and give them the best possible opportunities in life."
Anyone who has a spare room and is aged 21 or over can apply to be a foster carer.
Information sessions will take place at Crowthorne Library, in High Street, between 10am and noon on Wednesday, and at Finchampstead Children's Centre, in Gorse Ride North, between 5.30pm and 7.30pm.
An advice session will also be held at Sandhurst Memorial Park community hall from 11am to 2pm on Thursday May 23. If you are interested in becoming a foster carer, Berkshire authorities want to hear from you, either at www.facebook.com/FABerks or www.twitter.com/FABerks.
Alternatively, you can visit www.berkshirefostering.co.uk or by calling 01344 352000.