Social networking websites such as Facebook and MySpace encourage teenagers to build "transient relationships" that can leave them traumatised and even suicidal when they collapse, the head of the Roman Catholic Church in England and Wales warned today.
Archbishop of Westminster Vincent Nichols also expressed concern about the rise of individualism in society.
He described footballers who break their contracts to move to other clubs for bigger salaries as "mercenaries" and said moves to loosen laws on assisted suicide were particularly worrying.
His comments in The Sunday Telegraph follow the inquest into the death of 15-year-old Megan Gillan, a student at Macclesfield High School in Cheshire who took a fatal overdose of painkillers after being bullied on social networking site Bebo.
Archbishop Nichols said the sites encouraged young people to put too much emphasis on the number of friends they have rather than on the quality of their relationships.
"Among young people often a key factor in them committing suicide is the trauma of transient relationships," he said.
"They throw themselves into a friendship or network of friendships, then it collapses and they're desolate."
He continued: "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.
"But friendship is not a commodity, friendship is something that is hard work and enduring when it's right."
Archbishop Nichols said the internet and mobile phones were "dehumanising" community life and that relationships had been weakened by the decline in face-to-face meetings.
"I think there's a worry that an excessive use or an almost exclusive use of text and emails means that as a society we're losing some of the ability to build interpersonal communication that's necessary for living together and building a community.
"We're losing social skills, the human interaction skills, how to read a person's mood, to read their body language, how to be patient until the moment is right to make or press a point.
"Too much exclusive use of electronic information dehumanises what is a very, very important part of community life and living together."
The Archbishop, who is a supporter of Liverpool FC, said there was a loss of loyalty in society that was typified by the attitude of some footballers.
"What football spectators appreciate is a bit of loyalty and we're seeing that less and less.
"There are echelons of football, as in society, where some players are clearly mercenaries.
"I regret in a way that somehow the local identification, the local bonding between the community and its football team has been commercialised to such an extent."
He added that assisted suicide "seriously weakens the fabric of mutual responsibility within society".
"It leads to the idea that people who require a lot of care ought to be moved even further off of the scene.
"Once the principle that a human life is disposable by age or illness, then it won't be the sick person who is making the decision it will be somebody else who makes it for them."