Heather Erin Bloom, 33, is also wheelchair-bound and was first reported missing by her mother, who lives in New York, in June 2009.
Her mother is estranged from the sibling who cares for Bloom and has not been able to contact Bloom since 2005, despite many phone calls, police spokeswoman Sgt. Mary Kusmiss said.
Investigators visited Bloom's sibling at the sibling's Berkeley residence in March. Kusmiss said the sibling insisted that Bloom is doing well but refused to allow investigators to search the residence.
Now the sibling has moved away, and police have reached an impasse in their investigation into Bloom's whereabouts, Kusmiss said.
There is no indication that Bloom is the victim of neglect or a crime, but police want to ensure she is alive and well.
Bloom is described as a white adult female with brown hair and blue eyes. She is about 5 foot 7 inches tall, 140 pounds, and wheelchair-bound.