Amber Alert for 4-year-old Texas girl Maleah Davis, allegedly abducted by 3 men: Cops Maleah Davis, 4, was last seen by her family Saturday night, police said.

A frantic search was underway in Texas Sunday for a 4-year-old girl whose whose mother's ex-fiance told police she was kidnapped by three men, including one who knocked him out during a carjacking, authorities said.

An Amber Alert was issued on Sunday morning for Maleah Davis, a Houston girl who underwent brain surgery last month. She was last seen wearing a pink bow in her hair, a light blue zip-up jacket, blue jeans, and sneakers, police said.

Police are asking the public for help in finding the girl, who was last seen on Friday night when, according to what her her mother's former fiance, Derion Vence, 26, told police, three mystery men beat him up and briefly held him and her 1-year-old brother hostage. He later told police that they dumped him and the toddler on the side of the road and absconded with Maleah.

Sgt. Mark Holbrook of the Houston Police Department Homicide Division said Vence said that he went in and out of consciousness during the ordeal and, at one point, woke up to find the suspects driving him and the two children around in what he described as a blue pickup truck.

Vence told police that he eventually regained full consciousness around 6 p.m. on Saturday, waking up on the side of a road in the Houston suburb of Sugar Land with his toddler unharmed near his side.

But Maleah was nowhere to be found, Vence told police.

Holbrook said there is about a 21-hour gap between the alleged assault and when he woke up on the side of the road that Vence doesn't remember.

"We'd love the public to help us so we can fill in the blanks in this story. I realize there are a lot of blanks in that story, but we're hoping the public can fill in the blanks," Holbrook said during a news conference Sunday afternoon.

Holbrook declined to say if police are suspicious of Vence's story. But he noted that investigators have not found any evidence, including security video or independent witnesses, to corroborate the Vence's story.

"I don't want to speculate," he said, explaining the purpose of Sunday's news conference is to get the public to help "to figure out what really happened."

Vence told police he was driving with the children to pick up their mother Friday night at George Bush Intercontinental Airport when he noticed something wrong with their car, a 2011 silver Nissan Altima, and pulled over in north Houston, Holbrook said.

"He hears a popping noise like he has a flat tire, pulls over to check on it," Holbrook said. "According to Derion, what happens next is a blue pickup truck pulls up behind him, two Hispanic males get out. One of them makes a comment, saying that Maleah looks very nice, looks very sweet. The other male hits Derion in the head. Derion loses consciousness."

Vence told police that he kept going in and out of consciousness, but at one point he was in the back of the suspects' truck with his son and Maleah and that there were now three suspects in the vehicle driving them around, Holbrook said. He said the next time Vence woke up, about 6 p.m. on Saturday, he was on the side of the Southwest Freeway near State Highway 6 in Sugar Land, some 22 miles southwest of Houston.

"He wakes up. He has his son ... with him. He begins walking around. He tries to summon help. Nobody's really helping him," Holbrook said, recounting Vence's account.

He said Vence told police that he walked with his son to Houston Methodist Sugar Land Hospital, arriving about 10 or 11 p.m. He was treated for a head injury and police were called.

He said police have also put out an all-points bulletin for the family's silver Nissan, which is registered to Maleah's mother and has a paper dealer's plate number 330-92G9.

Holbrook said the Nissan was spotted by a traffic camera at an intersection in Sugar Land at 2:54 p.m. on Saturday.

He added that Vence described the suspects' pickup truck as a 2010 Chevrolet crew cab.

Maleah's mother, meanwhile, arrived at the airport from a trip to Massachusetts and didn't find Vence there to pick her up, Holbrook said. That's when she called a relative to come and get her, but never reported Vence or her children missing, Holbrook added.

Maleah has had several brain surgeries, Holbrook told reporters at the news conference; including one that was performed last month.

"She needs a lot of care and she was sick this week, too," Holbrook said.

Anyone with information on Maleah's whereabouts is urged to contact the Houston Police Department at (713) 308-3600 or Crime Stoppers at (713) 222-TIPS.

ABC News' Stacy Chen contributed to this report.

Editor's note: This story has been updated to reflect changes in the spelling of Derion Vence's name and his relationship to Meleah Davis' mother, which were initially based on information provided by the Houston Police Department.