The family of five-year-old April Jones say they are "shattered" by her disappearance and have appealed for her safe return.
A 46-year-old man - named by Sky sources as Mark Bridger - has been arrested on suspicion of her abduction. Police said they had been "actively looking for him".
Detectives said the search is continuing for the little girl who was last seen playing on her bicycle with friends near her home in the Bryn Y Gog estate in Machynlleth, mid Wales, at around 7pm on Monday.
She was last spotted by another child getting into a grey or light-coloured van - similar to a Ford Transit Connect or Land Rover-type vehicle.
A statement released on behalf of her parents, Paul, 43, and Coral, 40, said their "lives were shattered when our beautiful little girl April who was playing with friends was taken from us".
"We are devastated and our lives have stopped," the statement said. "Please, please if you have our little girl, let her come home to us."
Detective Superintendent Reg Bevan, of Dyfed-Powys Police, said they are examining the arrested man's left-hand drive Land Rover Discovery.
He said the suspect is a local man and was walking by the side of the road, a couple of miles outside the small town, when he was seized at around 3.30pm.
Detectives were due to interview the suspect at Aberystwyth Police Station.
A massive search has been under way since April went missing. Overnight, police set up roadblocks around the town and checked cars. Two helicopters have been scouring the area along with dogs.
Hundreds of residents have been helping in the search and are co-ordinating their efforts at the Machynlleth Leisure Centre.
Superintendent Ian John said specialist police officers and mountain rescue would be searching through last night.
"We ask the public to take this opportunity to have some rest and if they're available to consider coming and helping us again (on Wednesday)," he said. "The residents have really shown themselves to be a very close-knit and kind hearted community."
April has a brother Harley, who is nine or ten, and a 16-year-old sister Jasmine, who has also been helping with the search.
Her godmother Mair Raftree, 41, from Aberystwyth, wept as she told Sky News about the family's distress. She said they are hoping "April will be returned safe and well".
She added: "She's lovely, she's got a nice little character. We just want her back."
Police are also looking at whether her disappearance is linked to another attempted abduction in the Aberystwyth area a week ago.
April was wearing a purple knee-length coat with grey fur around the hood, a white polo top, and black trousers, when she was abducted.
A huge appeal has been launched on Twitter, with many celebrities tweeting and re-tweeting the message. Her poster is also being circulated on Facebook.
During an earlier news conference, Mr Bevan said April got into the driver's side of the van. It means she could have got in with the driver or the vehicle was a left-hand drive.
"The indications are that she got into the vehicle willingly ... It's very difficult to give an exact account of what happened. There's nothing to suggest at this stage that there was a struggle when she got into the car," he said.
He also emphasised the difficulties of getting accurate information from the young children who were playing with April when she disappeared.
Police have asked anyone with information to call them on 0300 200 0333.