CHARLOTTESVILLE, Virginia (AP) — The parents of a missing University of Virginia student appealed Saturday for whoever is responsible for her disappearance three weeks ago to help them find their daughter.

Sue and John Graham, whose 18-year-old British-born daughter Hannah disappeared on Sept. 13, issued a written and videotaped statement describing the case as a nightmare and noting that despite thousands of tips from the public, the college sophomore has not been found.

"Somebody listening to me today either knows where Hannah is, or knows someone who has that information. We appeal to you to come forward and tell us where Hannah can be found," Sue Graham said in the taped statement. "John has already said that this is every parent's worst nightmare ... Please, please, please help end this nightmare for all of us. Please help us to bring Hannah home."

Both parents wore blue collared shirts, along with buttons bearing their daughter's picture and orange ribbons. Sue Graham took deep breaths and read her statement with a shaky voice, fighting back tears as her husband put his arm around her several times.

Jesse Leroy Matthew Jr., a former college football lineman and sometime cab driver, has been charged with "abduction with intent to defile" in the disappearance. Police say forensic evidence also connects the 32-year-old Charlottesville man to the 2009 slaying of Morgan Harrington, a 20-year-old Virginia Tech student.

The Grahams thanked the investigators as well as members of the public who have offered support.

A search team of about 110 people including law enforcement officers and trained volunteers was combing through fields and countryside around Charlottesville on Saturday. Searchers have been out every day since the student was reported missing Sept. 14.

Mark Eggeman, search and rescue coordinator for the Virginia Department of Emergency Management, said his team was focusing on 200 square miles (520 square kilometers) surrounding downtown Charlottesville and had covered just under half of that ground. A law enforcement computer mapping specialist has been brought in to help the team piece together the areas it has covered into a master planning map.

"It's a lot about just trying to connect dots," he said.

A plane was taking high definition images on Saturday of areas on the west and east sides of town, which will then be scanned and analyzed with computer software. An unmanned drone was used earlier in the week to survey an area where power lines would have made it difficult to fly a plane or helicopter.

Despite the technology, the backbone of the search is still the officers trudging through fields and walking along creek beds.

"It still takes boots on the ground," said Eggeman, who's been involved in search and rescue operations for 30 years. "Despite what you see on 'CSI,' and everything else, you still have to do it the old fashioned way."

Uniformed officers riding ATVs were seen combing farmland earlier this week, checking fence lines and a well. They've also ventured into some mountainous terrain, but investigators decline to share specifics about exactly where they are focusing.

With archery hunting season for deer starting Saturday, hunters also have been asked to be alert for any signs of Graham. Authorities also have asked farmers and property owners to check their land. Searchers have gotten over 3,500 tips, which are screened by detectives for usefulness.

Asked how long the search would continue, Eggeman said that searchers wouldn't consider stopping until they've met their objectives and that the decision would ultimately be led by Charlottesville Police Chief Timothy Longo.

Eggeman also was involved in the search for Harrington. Hundreds of volunteers helped search for that woman, and her remains were eventually found by a farmer inspecting his property about three months after she went missing. The field was in the rugged foothills of the Blue Ridge Mountains about 10 miles (16 kilometers) from the concert venue she disappeared from.