Archbishop Vincent Nichols said MySpace and Facebook led young people to seek "transient" friendships, with quantity becoming more important than quality.
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 the Sunday Telegraph newspaper.
He added: "Friendship is something that is hard work and enduring when it's right".
Archbishop Nichols said society was losing some of its ability to build communities through inter-personal communication, as the result of excessive use of texts and e-mails rather than face-to-face meetings or telephone conversations.
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.
Archbishop Nichols said that social networking sites such as Facebook and MySpace encouraged a form of communication that was not in his words "rounded", and would not therefore build rounded communities.
I agree with some of his statements here but I seriously doubt that any sociologist or psychologist would say with any certainty that suicide can be linked with frequent use of social networking.