The search for Serenity Dennard had been stalled for two days before resuming Friday because of a winter storm. The girl went missing Sunday in subfreezing temperatures from the Black Hills Children's Home near Rockerville.
The Pennington County Sheriff's Office said if the girl was outside, it's unlikely she survived because she wasn't dressed for the weather. Authorities said their efforts are now focused on finding her body.
On Friday, searchers headed outside with specially trained dogs to go over the area near the children's home. Additional dogs and handlers are expected to arrive from out-of-state for the weekend.
The home is operated by Children's Home Society.
The Rapid City Journal reported Friday that staff at the facility waited more than an hour and a half before calling 911 after Serenity ran away.
Bill Colson, executive director of the Children's Home Society, said that after Serenity left the sight of a staff member at about 10:45 a.m., "we immediately conducted a thorough search of our grounds and buildings. When we were unable to find Serenity we called law enforcement."
Helene Duhamel, spokeswoman with the Pennington County Sheriff's Office, said investigators believe someone heading to the Children's Home around 11 a.m. was probably the last person to see the girl.