Police are urging teenagers to remove their profile pictures and personal details from Facebook after a man was charged with the murder of a young Sydney woman last week.

It is alleged that Nona Belomesoff, 18, believed she was going to work with an animal welfare organisation when she left her home last Wednesday to meet two men she befriended on Facebook.

Her body was found in a creek bed in Sydney's south-west on Friday and police have charged a 20-year-old man with her murder.

Police say the second man Ms Belomesoff believed she was meeting did not exist.

The man charged with murder allegedly set up a false Facebook profile masquerading as someone who worked with animals.

The case has ignited debate on the issue of cyber safety and security, particularly when it comes to younger people.

Although the majority of friends on a Facebook user's list are people they know, it is relatively easy to make new friends online.

Detective Superintendent Peter Crawford is with Queensland's Task Force Argos, which targets online predators. He says there is no reason a teenager or a child should have a photo on their Facebook profile page.

He says photos, school details, or a young person's date of birth should never be posted on the social networking site.

"If you use social networking as a closed networking with friends that you know... then the risks are very much reduced," he told ABC Local Radio.

"[But] if you post private information ... you are leaving yourself very much exposed not just to these types of offences, but also to fraud."

Every month, the police task force receives at least one complaint in relation to online offenders, but covert police posing as children online can be hit upon regularly.

Users must be at least 13 years of age to sign on to Facebook, but a child can easily sign up for a profile by altering their date of birth.

Facebook's 'great betrayal'

In November last year, Facebook fine-tuned its privacy settings so a user could control each individual area of their profile.

The change allowed Facebook users to decide whether to list details such as photos or posts, for example, as visible to friends, friends of friends, or to anyone.

But the onus is on the user to change their settings from open to private, which means some people may not even realise how much information they're sharing to the outside world.

ABC technology editor Peter Marks say although Facebook cannot be blamed for Ms Belomesoff's death, it could have provided a platform for her to meet her alleged killer online.

"Unfortunately the default privacy settings on Facebook have historically been rather low, which means by default that things kids load up onto Facebook - their photos for example - are publicly available to people who aren't their friends," he said.

"[Facebook] actually made things like lists of friends publicly available so when they did the upgrade they opted people in - they didn't ask you to accept the extra publicity that you were getting.

"Basically this has been called Facebook's great betrayal."

He says many young children may think they are only sharing their private photos with friends, but their images could be available to the public - and stalkers - via Google.

Mr Marks also warns parents and young people about fake people on Facebook, or "mistaken identities".

"They may be a made-up identity designed to entrap you, as it appears may have happened in this case," he said.

"Facebook is really not like meeting someone down at the park, or meeting someone at the club or something."