Sabrina Ramirez was last seen at about 7 a.m. Friday morning and was not at home when her mother returned from work that night, according to police.
Her mother reported that Ramirez' backpack, some clothes and her favorite hair gel were also missing and said the girl has run away in the past, police said.
The mother attempted to send a text message to Ramirez, who usually responds to the messages, but did not immediately receive a reply from the girl.
Ramirez sent text messages to her family Sunday, indicating that she may not be voluntarily missing, but police said there was nothing to substantiate the messages.
Ramirez is deaf in both ears and will not respond to verbal communication. She has recently talked about issues relating to depression, police said.
She is described as a Hispanic girl, 5 feet 1 inch and about 115 pounds. She has green eyes and black hair with red highlights.
Anyone with information regarding Ramirez' whereabouts is asked to call Union City police at (510) 471-1365.