Top social networking sites like Facebook and LinkedIn may be well-established, but that doesn’t mean they’ve stopped growing.
Nearly half of the biggest social networking sites are also among the fastest growing, according to data released Wednesday by Nielsen Online.
These top sites have also expanded beyond the youthful audience the social networking space initially captured — to find a place in older visitors’ professional lives.  Facebook, LinkedIn, and Reunion.com are most popular among visitors ages 25-34, 35-49, and 55-64, respectively, Nielsen reported.

Rank
(by Sept. YOY UA growth)
10 Fastest Growing
Social Networking Sites: Sept. 2008
Sept. 2007:
Unique Audience …

British 18- to 20-year-olds most commonly visit student finance websites, while teens in the UK favor mobile social networking and online gaming sites, and children prefer fashion and entertainment sites, the Times of London and Brand Republic reported last week. 
Those results come from a recent Nielsen study that surveyed 40,000 British Internet users and identified websites with the highest concentrations of users in particular age groups.
Nearly half of all unique visitors (40%) to the websites for Student Loans Company, UCAS, and Student Finance Direct were between the ages of 18 and 22, Nielsen …