Across cyber space, young people are living in a world where fantasy and reality collide.

Just how dangerous or disturbing this can be has been demonstrated by two cases in the past week. A 15-year-old boy used his blog to reveal his suicide intentions before jumping from a Kennedy Town rooftop. A few days earlier a PE teacher pleaded guilty to having unlawful sexual intercourse with a 12-year-old he had lured through an online chat room.

Other high-profile incidents have raised the alarm, not just in Hong Kong. Earlier this summer 17-year-old Katherine Lester ran away from her home in the US state of Michigan to meet up with Abdullah Jimzawi, 20, a Palestinian in the West Bank town of Jericho, after the two fell in love on MySpace. Jordanian authorities sent her home.

From serious incidents to trivial but malicious gossip, educators and parents are having to figure out how to respond to the cyberworld teenagers increasingly inhabit.

Should teachers and administrators monitor sites such as MySpace, Xanga and Facebook? Where does a school's responsibility begin and end when it comes to online networking that can involve cyber bullying, slander and the chronicling of sexual exploits and alcohol and drug abuse?

Lisa Leung Yuk-ming, assistant professor in the department of cultural studies at Lingnan University, said that under the cloak of virtual identities, blogging could encourage extreme behaviour. 'One casual word in cyberspace might result in someone killing themselves,' she said. However, there was no way of predicting whether young people would act on the disturbing messages they posted.

Although she described the sites of many young Hong Kong people as a 'narcissistic indulgence' she does not see them as inherently unhealthy. Instead, she urged friends, family and teachers who might read worrying messages to respond through traditional forms of communication, in the real world.

She and other social scientists said that there was no stopping this new form of communication. 'It is something we have to deal with because it is the medium of the future,' she said.

Ben Chung Kam-lun, 17-year-old chairman of the Hong Kong Secondary Students' Union, said Xanga was the most popular site among local students and that while most used it responsibly, there were many cases of misuse.

'Students lie in their comments about other students. They use [the site] to insult others,' he said.

In Hong Kong, schools have taken action against sites that involve bullying of named individuals or affect their reputations. For instance, a 15-year-old Sha Tin College boy was expelled in 2004 for hosting an internet forum criticising the school. The English Schools Foundation and other international schools normally block access to teen sites on campus. But what goes on at home is harder to control and schools go no further than issuing warnings and guidance to students and their parents on how to play safe on the net.

Island School runs lessons on the dos and don'ts on the internet. But Andy Statham, its head of IT, added: 'Other than that, we have no specific policy. Personally, I don't think we need policies. We should try to educate students into using the internet in a sensible way.'

John Wray, principal of South Island School, ruled out monitoring such sites, not only because of the difficulties involved but also because 'there needs to be a degree of trust'. Schools should not try to play the role of cyber police, he said.

He did, however, hold students responsible for their cyber transgressions if they were brought to the school's attention. He declined to discuss specific offences, but said: 'We've had a number of such cases. The punishment has been as severe as suspension.'

Parents needed to be partners in cyber education, monitoring what went on a home. On the whole, he said, the creativity and personal expression on teen blogs should be encouraged: 'It's a positive thing overall but there are dangers we need to be aware of.'

Teachers at Australian International School also made a point of teaching students how to be responsible on the internet, according to Howard West, its assistant principal of student services. There had still been instances of students posting hurtful or inflammatory comments, he said. 'We have to deal with those complications, so that's where the dialogue between home and school intensifies.'

Mr West said AIS teachers had noticed that students became more responsible internet users as they got older. Problems occurred mostly with 12 to 15-year-olds.

At Hong Kong International School, discussion about teen sites had become a regular part of the curriculum in technology classes, but secondary-school IT director David Elliott said: 'Students don't seem to understand how public they are. They think that bragging about risky behaviour is OK because the internet is somehow not real. The opposite is the case. The internet is very real.'

Lee Tak-yan, a social scientist at City University who specialises in teen issues, said that one of the attractions of blog sites was that they provided a forum where teenagers could control the image they projected of themselves, making them socially safer than unpredictable face-to-face communications. 'One of their basic needs is wanting someone to know them,' he said.

Parents should not pry into this virtual world, any more than they should try to read a child's personal diary. Instead, they should seek real contact with their teenagers.

As for wider control, he sees no role for it, because that would impinge on basic freedom of speech.

MySpace and Xanga offer safety tips to parents at the following sites: