The Nielsen survey of users' habits found that 67% of all those going online were spending time at social network and blogging sites.
Interest in the category is growing four times faster than the other top four sectors, said the report.
In the UK one in every six minutes of the average web user is spent at a social site, it found.
"Social networking has become a fundamental part of the global online experience," said John Burbank, chief executive of Nielsen Online in a statement."Social networking will continue to alter not just the global online landscape, but the consumer experience at large," he said.