"For some reason, suicidal behaviour does seem to be something that it's a contagious idea that young people are particularly prone to, not all young people but young people who are vulnerable and distressed and struggling.
"Talking about it, whether in social media or in other ways, might add to that."
However, there was no good evidence that the emergence of social media had led to an increase in suicide, said Dr Watson.
He was the facilitator of a panel discussion on social and new media yesterday at the conference of the organisation Suicide Prevention Information New Zealand.
The theme of the conference was "How do we talk about suicide?"
Panel member Chris Banks, the Mental Health Foundation's communications officer and a blogger on mental health issues, described how social and new media could provide direct access for organisations such as the foundation to people who might need its help.
He said readers of his blog had at times replied on the website with "quite depressed or potentially suicidal thoughts. I have suggested messages of support and you can help challenge their thinking, online.
"They might be posting on a public space online. It's an opportunity to engage with them."
After the deaths of four teenagers in Masterton and Pahiatua, a Facebook page had been created that was open to all Facebook account holders.
"People are speculating on the mode of death and whether there was a suicide pact. At a community level there's public meetings to help dispel those rumours and help get people the real information. In social media you have the opportunity to provide information."
He had posted links on the Facebook page that took viewers to website-based help and support information and a video about coping after the suicide of someone close.
Where to get help
* If it's an emergency and you feel like you or someone else is at risk, call 111. Or call Youthline 0800 376 633, Lifeline 0800 543 354, Depression Helpline 0800 111 757, What's Up 0800 942 8787 (noon-midnight).
* Suicide Prevention Information New Zealand has more information. Visit: www.spinz.org.nz.
* The Ministry of Health also offers information at www.depression.org.nz and www.thelowdown.co.nz.