The spiritual leader of the four million Roman Catholics in England and Wales has damned social network sites, accusing them of undermining community life and leading teenagers to suicide.

Archbishop of Westminster Vincent Nichols said MySpace and Facebook led young people to seek "transient" friendships, with quantity becoming more important than quality. MySpace is owned by News Corp, parent company of The Times.

He said a key factor in suicide among young people was the trauma caused when such loose relationships collapsed.

"Friendship is not a commodity," he told said. "Friendship is something that is hard work and enduring when it's right".

Archbishop Nichols said that social networking sites such as Facebook and MySpace encouraged a form of communication that was not "rounded", and would not therefore build rounded communities. He said young people were being encouraged to build up collections of friends as commodities, that these friendships could easily collapse, and teenagers were left desolate when they did.

Arguing that society was losing some of its ability to build communities through inter-personal communication because of the result of excessive use of texts and e-mails rather than face-to-face meetings or telephone conversations, he said too much emphasis was placed on the number of "friends" a person has rather than the quality of those friendships.

He said skills such as reading a person's mood and body language were in decline, and that exclusive use of electronic information had a "dehumanising" effect on community life.

"Facebook and MySpace might contribute towards communities, but I'm wary about it," he said.

"Among young people often a key factor in their committing suicide is the trauma of transient relationships. They throw themselves into a friendship or network of friendships, then it collapses and they're desolate.

"It's an all-or-nothing syndrome that you have to have in an attempt to shore up an identity; a collection of friends about whom you can talk and even boast."

His argument that the internet and mobile phones are "dehumanising" community life come after the death of 15-year-old schoolgirl Megan Gillan, who took a fatal overdose of painkillers last week after being bullied on Bebo, another networking site.

He also voiced his concerns about the loss of loyalty and the rise of individualism in British society, singling out footballers for acting like "mercenaries".

There is a Vincent Nichols claiming to be Archbishop of Westminster and giving the correct home address in Ambrosden Avenue, Westminster, on Facebook, with 336 friends. The Times is awaiting confirmation from the Archbishop's spokesman that this page is genuinely that of the real Archbishop Nichols.