The search for an eleven-year-old from Bispingen in Lower Saxony was unsuccessful on Tuesday night.
The police announced this early in the morning.
The girl has been missing since Sunday noon.
The 35-year-old mother and her four-year-old son were found dead in a house on Sunday.
The police released a photo of the eleven-year-old.
The police and the public prosecutor announced on Monday that mother and son had shown traces of the use of external violence.
According to the information, an urgent suspect was arrested on Sunday afternoon in Schneverdingen (Heidekreis), about 20 kilometers away.
It is the life companion of the killed.
The 34-year-old German is in custody.
He did not provide any information on the matter.
"For tactical reasons, there is currently no information on the current track record and specific investigative measures," said a spokesman for the prosecutor on Monday evening.
The search for the daughter will continue with high pressure.
In connection with the missing child, the police seized the suspect's vehicle with a license plate from Diepholz.