The body of the shy British teen was found on a remote farm in October with her arms bound and duct tape covering her mouth. The girl had been raped and murdered by someone she met on Facebook.
"If you're an overweight girl living in England and doesn't have someone to love her, you will look for that and you will grab at that, and the predators know that," said Parry Aftab, executive director of Wired Safety, a leading Internet safety Web site.
Peter Chapman, a 33-year-old convicted rapist, was arrested after Hall's death on an unrelated charge and confessed to Ashleigh's murder.
"I killed somebody last night," Chapman told police. "I need to tell someone from CID where the body is."
Chapman posed online as a handsome teenage boy, befriended Ashleigh on Facebook and other Web sites and sent her flattering messages, telling her she was "sexy as hell." Eventually, they arranged to meet.
Ashleigh told her mother she was attending a sleepover, according to the Telegraph, but instead went to meet Chapman, who said he raped and suffocated her in his car, and then dumped her body in a field.
The murder prompted the famously opinionated British press to call for action. Britain's Child Exploitation and Online Protection Centre, CEOPS -- an organization dedicated to eradicating all forms of child sexual abuse -- claimed that in the first quarter of the year it received 253 complaints about Facebook; 39 percent of them were suspected cases of kids being groomed online by pedophiles.
In December, Facebook, the world's most popular social networking site, created a Global Safety Advisory Board to tackle issues such as online stalking and cyber-bullying among its 400 million users.
Serious crimes are rare, but when they happen, they capture headlines. Last year, a British man dubbed the "Facebook Murderer" trawled the Internet searching for victims, according to police.
Last month, 25-year-old Paul Bristol was jailed for murdering his ex-girlfriend after seeing a photograph of her on Facebook with another man.
A nursery worker in southern England recently pled guilty to photographing horrific acts of abuse she carried out on children in her care and sending the images to a man and a woman she met on Facebook and other social networking sites.
Facebook Revamps 'Safety Center'
Facebook launched a redesigned "Safety Center," agreed to establish a 24-hour hotline to improve the way abuse is reported, and pledged money to educate users -- particularly younger users -- about predators and cyber-bullies lurking on the Web.
The safety improvements failed to satisfy CEOPS, which had argued that a "panic" button should be placed on every Facebook profile page linking directly to resources that can help and to contacts for local law enforcement.
Facebook officials rejected CEOPS' request to institute the "panic" button, as other sites have done.
"We asked Facebook to take the button in the same way as Bebo, and AOL, MSN and others had and put it into their environment so that children could report to us when there were afraid in the online environment. They chose not to do that," said CEOP head Jim Gamble.
Ashleigh Hall's mother, Andrea, has taken up the cause to protect young users from predators on social networking sites so that no other families go through what the Halls did.
"All the other sites have got it on. So why hasn't Facebook got it on?" she said.
Facebook declined "Nightline's" request for an interview, but sent a statement by e-mail: "Our experience affirms there is no single answer or silver bullet that makes the Internet or Facebook safer. We think the investments and partnerships we announced earlier this week in the U.K. will transform social networking safety and security... We look forward to rolling out similar programs around the world."
Parry Aftab, an Internet safety expert and adviser to Facebook, said she believes the social networking site is doing all it can. The rest, she said, is up to users.
"Bottom line: it's making sure the information users need to keep themselves safe is there and they know when to reach out to law enforcement and get help," Aftab said.
Police who investigated Ashleigh Hall's murder agree that users must be aware and make wise choices.
"Our message is: do not meet people that you've only met on social networking sites," said Andy Reddick, chief superintendant of the Durham police. "But I'm also a realist. I know what people will still go on and do that. So there's preventative messages that you need to listen to and that is: If you're going to meet someone, tell someone where you're going to meet them, tell them who you're going to meet and only meet them in very, very public places."