More than 100 neighbours, friends and family members have joined the 80 police hunting for Rosie Palmer, who went missing on Thursday afternoon from the Headland area of the town.
Coastguard teams combed the shoreline and nearby cliff-tops, assisted by the Northumbria police helicopter, and co-ordinated a sea- search by the Sunderland lifeboat, inshore rescue craft and fishing vessels.
But Detective Chief Inspector Ray Mallon, leading the investigation, said he could not rule out the possibility that she had been abducted, although he was keeping an open mind.
The girl's mother, Beverley, made an emotional appeal for her return at a news conference yesterday, begging anyone who might be holding Rosie to let her go.
'I just want my little girl back,' she said.
'She is only three and if someone has got her, please let her go. If anyone knows where she is, or if someone has seen her, please tell the police, I beg you.'
The search area widened as the concern of police and residents grew with each hour.
No clues emerged as to her disappearance within 10 yards of her home.
Rosie, who attends St Helens Nursery, was collected by her stepfather, John Thornton, at 2.40pm and taken home where she played with some friends until she heard the ice-cream van.
Wearing red and white gingham shorts, a white T-shirt with a daisy motif on the front, white training shoes, a red baseball cap and spectacles, she was last seen by her mother who had given her money to buy an ice-cream at 3.30pm.
She bought an ice lolly but then vanished. Neighbours quickly began looking for her, but the police were not told until just after 8.30pm.
Her mother, a midwife who works part time at Hartlepool hospital, moved to Bristol several years ago where she met her husband, Martin, a commercial lawyer.
But shortly after Rosie's birth they split up and Mrs Palmer returned to Hartlepool, where she lives with Mr Thornton, 46.
Mr Palmer kept in regular touch with his daughter and was said to be distraught at her disappearance. Two detectives yesterday travelled to Bristol to meet him, although officers said there was nothing to suggest that he was involved.
Det Chief Insp Mallon praised the efforts of local residents who were stunned by the disappearance.
He said: 'We have received tremendous support from local people. As the news of Rosie's disappearance spread we were overwhelmed by the number of residents who have helped us search throughout the night.'
He described Hartlepool as 'quite a small, tight-knit community' and appealed to everyone to check their gardens, sheds and outhouses for the little girl.
Later, Detective Superintendent Doug Smith said police had received a report of a previous abduction attempt near Rosie's home last year, and were investigating possible links. 'We are also making inquiries about whether any suspicious characters have been seen in the area,' he added.