(CNN) -- The desperate hunt for a 5-year-old girl abducted in Wales entered its fourth day Thursday, with hundreds of police officers, volunteers and mountain rescue workers combing a rural area for any trace of April Jones.
Police continue to question a man arrested on suspicion of her abduction but said they urgently need help from the public to trace his movements during the crucial hours after April was snatched from a street Monday.
Mark Bridger, 46, remains in police custody and will be questioned again Thursday, said Detective Superintendent Reg Bevan, of Dyfed-Powys Police.
A team of officers is working around the clock to try to piece together Bridger's movements between Monday evening and his arrest Tuesday afternoon, Bevan said, using forensic analysis and witness statements.
But, he said, more help is still needed from people who may have seen or spoken with Bridger at that time.
"We are appealing for anyone who has had contact with Mark; we don't have the complete picture yet," Bevan said.
British Prime Minister David Cameron added his voice Thursday to the plea for information made by April's family, an unusual intervention by the country's leader in an ongoing police search.
"My heart goes out to April Jones's family. I appeal for anyone who saw or heard anything to talk to the police," he said via his official Twitter feed.
Speaking at Downing Street, Cameron also mentioned the extra concern prompted by the news that April has cerebral palsy, a condition his late son Ivan also suffered.
The girl's abduction as she played with a friend on a street near her home in Machynlleth, mid-Wales, has shocked the small, close-knit community -- and made headlines across the United Kingdom.
There has been no trace of the pretty brown-haired child since she was seen Monday evening, climbing into a vehicle that then drove off.
April's mother, Coral Jones, made an emotional televised plea for help Wednesday.
"It has been 36 hours since our April was taken from us," she said, breaking down in tears. "There must be someone out there who knows where she is and can help the police find her.
"We are desperate for any news -- April is only 5 years old. Please, please help us find her."
Local volunteers have joined police and rescue teams in searching the town and surrounding area, a task made more difficult by poor weather, flooding rivers and hilly terrain.
Police said Wednesday that the search was focused on more than 20 different areas, including houses, outbuildings, river banks and open countryside.
"The geography is very challenging and everyone is working in a hostile environment -- by that I mean the terrain is difficult, waterlogged, working near to flooded rivers with the potential for mine shafts and unstable ground," police Superintendent Ian John said.
Police dogs, coast guard teams, kayakers and mountain rescue specialists have been called in to assist in the search.