FOND DU LAC COUNTY, Wis. (CBS 58) -- The Fond Du Lac County Sheriff's Office is working with the Milwaukee Police Department to locate a missing 17-year-old girl.

17-year-old Cassidy Schilcher has blonde hair and brown eyes. She's 5'8" and weighs 110 pounds.

A social media post from her foster mother, Shannon Siebert, says that Cassidy ran away on December 26. The post also explains that she suffers from mental illness and her family believes she is in danger.

The Fond Du Lac County Sheriff's office says the department continues to work with MPD and other agencies in the Milwaukee area to try and locate Cassidy.

Anyone with information regarding the case is asked to contact the Fond Du Lac County Sheriff's office at 920-929-3390.