London, UK - Of the 10,583,351 websites visited by UK Internet users in September, Facebook was the second most popular after Google UK. The number one social network in Britain received 3.16% of all UK Internet visits last month, equivalent to one in every 32. For the 4 weeks ending 27/09/08, one in every 50 UK Internet searches was for the single term ‘facebook’.

Facebook’s success in the UK (and many other markets) is undeniable, and - as the chart below illustrates - the growth hasn’t stopped yet. However, it has slowed: traffic to the site increased by 4% between August and September this year, down from 50% over the same period last year. The site’s annual growth rate remains impressive at 88% between September 2007 and 2008, but was significantly less than the 2905% it experienced the previous year.

Another ominous sign is that Facebook’s average session time has flattened out at 20 minutes; both MySpace and Bebo experienced a fall in average session time in tandem with their declining UK market share. So, Facebook has a while to go yet, but there is no doubt that its growth is slowing. Of course, social networking is about more than just one site – we recorded visits to over 7,000 during September – so what about the market as a whole?

UK Internet traffic to our Social Networking and Forums category increased by 0.3% between August and September, and it experienced growth rates of 3.5% and 4.2% respectively during August and July. However, to a certain extent this growth was seasonal, and looking at annual growth rates (e.g. September 2007 -2008) sheds more light on the topic.

The chart above illustrates the monthly annual growth rates (i.e. the increase in traffic compared with the same month during the previous year) for the category over the last two year. As you can see, growth peaked last autumn / winter at just over 70%, but has been declining during most of 2008. Between September 2007 and 2008 UK Internet traffic to the Social Networking and Forums category increased by 22% - it will be interesting to see for how long that number remains positive.

Robin Goad

Robin Goad is Research Director, Hitwise UK. This piece was originally published on Hitwise analyst blog here.

CC-licenced Flickr Image by Nathan Huth