TAMPA — An 11-year-old girl with Asperger's syndrome went missing from her east Hillsborough County home late Tuesday, sending scores of people on a search that began after daybreak and extended into Wednesday night.

Jenna Irmler, a sixth-grader at Nativity Catholic School in Brandon, was last seen by her family fixing a snack about 9 p.m. Tuesday, a Hillsborough County sheriff's spokeswoman said.

Parents Jason and Rebekah Irmler, who have three younger daughters, realized she was missing about 5:30 a.m. Wednesday, looked in the neighborhood and nearby woods for two hours and then called the Sheriff's Office. The Irmlers live in South Oak off Bell Shoals Road.

Sixty deputies and a band of parents stepped up the search, spreading out on foot, using boats, horses, dogs, bikes, helicopters and patrol cars, passing out fliers and at times calling out Jenna's name in a driving rain.

"She's 11 years old," Hillsborough sheriff's Col. Donna Lusczynski said at a 5:30 p.m. news conference. "It's getting dark. The weather is not very nice, so we're asking for people's assistance. If they see her, call 911. Get her to a safe place."

Jenna is 5 feet 2 and weighs 130 pounds, and has brown hair and brown eyes. She was last seen wearing a gray T-shirt and black sweat pants with a pink stripe down the side. Anyone with information is asked to call the Sheriff's Office at (813) 247-8200.

Lusczynski said the Irmler home at 515 Centerbrook Drive was being processed as a crime scene because of the nature of the incident, with investigators seeking clues to the disappearance. The parents are cooperating fully, she said. There was no sign of forced entry.

The Florida Department of Law Enforcement issued a statewide alert. No Amber Alert was issued because there was no clear sign Jenna was abducted, the colonel said.

A UPS driver reported seeing someone who may have been Jenna walk through the neighborhood after 9 p.m. Tuesday in the direction of the community's entrance. A tipster told the Sheriff's Office she might have been spotted hitchhiking on a nearby road.

It isn't unusual for Jenna to leave home for an hour, family told investigators. But this is the first time she's been missing so long. Usually her parents can quickly find her climbing trees in the woods across the street from her home.

Days ago, in a YouTube video, she took viewers on a trip through the woods as she walked and ruminated on her life.

"I do like walking out here," she said. "It does calm me down."

About 20 friends posted notes below the video Wednesday, telling her they missed her and were praying for her.

"Come back," one wrote. "Plz come back," wrote another. "Jenna, come back," a third wrote.

Multiple families from Nativity took off work to join the search and were directed by deputies to avoid areas where dogs were searching. The school's principal sent messages by phone Wednesday morning. Fliers were passed out to families at the school and posted on the school website.

Deputies checked on sexual predators within a 2-mile radius, 28 in all, and expected to expand the checks to a 5-mile radius. They searched libraries and parks where Jenna spends time and were reviewing security footage from nearby businesses.

George Zinto circled the Irmler family's neighborhood on his bicycle Wednesday afternoon, yelling her name as loudly as he could while suppressing tears. His son is in her class at Nativity.

"There was no way I could go to work today," Zinto said. "All I know is she is a sweet little girl."

Gundi Wanders and her son, a student at Bloomingdale High School, walked their neighborhood for two hours Wednesday before joining a nighttime search party at Beef 'O' Brady's organized by Nativity parents.

Wanders has lived in South Oak for 19 years and said the woods in the center of the neighborhood cover several square miles. Teenagers meet up in them to build campfires, and in the past homeless people have slept in the woods.

Also nearby is a marshy swamp with snakes and other potential dangers, she said.

"There's lots of places out here to hide, but (deputies) have been all over them," Wanders said. "It makes me sick to my stomach; I just hope she is okay."

The Sheriff's Office, from the first public notice of the disappearance, noted that Jenna has Asperger's. It's an often-used term for a high-functioning type of autism spectrum disorder. A sheriff's spokeswoman said the syndrome might keep Jenna from responding if strangers call her name.

Times senior news researcher John Martin contributed to this report. Contact Anastasia Dawson at (813) 226-3377 or adawson@tampabay.com. Follow @adawsonwrites.