Police looking for April Jones said they are trying to "piece together" Mark Bridger's movements around the time the five-year-old disappeared after they were given until 5pm on Friday to question him.
Detective Superintendent Reg Bevan from Dyfed Powys Police said 46-year-old Bridger would be interviewed again later on Thursday.
He told reporters at a press conference: "The investigation continues and our focus remains finding April.
"The investigation team will be interviewing Mark Bridger again and we will continue to piece together his movements during the relevant times and look to overlay his account with that we've gleaned from witnesses, sightings and the other inquiries that we are conducting."
April has been missing since about 7pm on Monday when she vanished while playing with friends.
Mr Bevan said a "vast" amount of forensic analysis is being carried out, forming a "crucial part" of the inquiry, but this alone would not find the little girl.
"Again I make an appeal to the public to help us find April, and in particular we are looking to trace the movements of Mark Bridger between 6.30pm on Monday and 3.30pm on Tuesday of this week and any sightings of him between these times," Mr Bevan said. "If anyone has had contact with him during this period, we urge you to come forward - and by contact I mean face-to-face contact, telephone contact, texting, social media, any contact whatsoever."
Police are also appealing for information about his blue Land Rover Discovery, registration number L503 MEP.
Superintendent Ian John said that he understood why volunteers wanted to help in the search for April and asked for people to come forward with their contact details and any specialist skills that they may have.
He also asked the public to search their immediate surroundings including gardens and outbuildings. Specialist police search teams are being helped by a marine unit, mountain rescue, the coastguard and lifeboat services. He said the search operation is "one of the largest of its kind in recent history", and that with police co-ordination, volunteers can be used "in the right place at the right time".