NEW YORK - Spending more time on social networks and blogs? You're not alone, with the latest figures showing the number of minutes spent on social networking sites in the United States has almost doubled over the past year.

Nielsen Online, which measures web traffic, said the number of minutes on social networks in the United States rose 83 percent in April from the same month a year ago, but found users were quick to move on and sites could quickly fall from favor.

Nielsen Online spokesman Jon Gibs said a major trend had been the continuing popularity of Facebook, which has more than 200 million active members and has become so mainstream it now hosts Pope Benedict and a list of world leaders.

News Corp's MySpace was second most popular but the number of minutes spent on this site fell 31 percent to 4.97 billion from 7.3 billion a year ago, although it remained the top social networking site when ranked by video streams.

Blogger, Tagged.com and Twitter.com came third, fourth and fifth respectively, with the number of minutes spent on Twitter - that lets people send 140-character messages or Tweets - rocketing 3,712 percent in April from a year ago.

"We have seen some major growth in Facebook during the past year, and a subsequent decline in MySpace," said Gibs in a statement.

Facebook came second to MySpace in rankings of video streams followed by Stickam, FunniestStuff.net and Funny or Die.

Gibs said Twitter had also come on the scene in an explosive way, perhaps changing the outlook for the entire social networking business.

"The one thing that is clear about social networking is that regardless of how fast a site is growing or how big it is, it can quickly fall out of favor with consumers," said Gibs.

"Remember Friendster? Remember when MySpace was an unbeatable force? Neither Facebook nor Twitter are immune. Consumers have shown that they are willing to pick up their networks and move them to another platform, seemingly at a moment's notice."

Figures from Nielsen released in April shows that more than 60 percent of Twitter users stopped using the free site a month after joining.

Facebook and Twitter are privately owned, although Microsoft bought a 1.6 percent stake in the company in 2007 and both are constantly the source of investment and buyout speculation.