According to Danah Boyd of Berkeley University and Nicole Ellison of Michigan State University, the first recognizable social network site (SNS), SixDegrees, was launched in 1997.

It was the first site to combine the features of creating profiles, listing “friends” and surfing their “friends’’ lists. Millions of users converged on SixDegrees, but the site eventually closed down in 2000.
 

2001 saw the second wave of SNSs, with the launch of Ryze.com. This and other sites like LinkedIn were intended to help people leverage their business networks. However, Ryze never became very popular, while LinkedIn became a significant business service.
 

Friendster started up in 2002 to complement Ryze, but as a social network rather than a business-oriented one. Friendster quickly became popular, but when the press started noticing it, its popularity exploded to such an extent that it didn’t have the capacity to handle it. When it consequently began to restrict activities, its popularity collapsed in the US, though it continued to attract users in South-East Asia.
 

Starting in 2003, a whole series of SNSs were launched, many based on shared interests (travel, church, pets, etc.). At this time, websites focused on media sharing started metamorphosing into SNSs–Flickr (photo sharing), Last.FM (music sharing), and YouTube (video sharing) being the prime examples.

Enter MySpace

Not too many people noticed when MySpace started up in 2003. And it was not launched with bands in mind, though they were welcomed. “Bands were not the sole source of MySpace growth,” Boyd/Ellison point out, “but the symbiotic relationship between bands and fans helped MySpace expand.” Not surprisingly, “teenagers began joining en masse in 2004.”

While MySpace became very popular in the US, others were doing well elsewhere. Orkut in Brazil and India, Mixi in Japan, LunarStorm in Sweden, and Cyworld in Korea, while Bebo became the leading European site. At the same time, other SNSs were created to support niche groups. This was the case of Facebook, which was designed for college networks only. Facebook began in 2004 as a Harvard-only SNS. “In 2005, Facebook expanded to include high school students, professionals inside corporate networks, and, eventually, everyone,” Boyd /Ellison observe. The rest is history.

Today, it is not known how many people use SNSs, though clearly they are still growing exponentially, particularly in the US, but also elsewhere. As of June 2007, Facebook visitors increased 270% year-on-year and Tagged an incredible 770% (though from a much smaller base). Not one of the major sites is growing at less than 50% (source: ComScore). How long can this last?