I'm looking for statistics that say what percentage of people use 1 or
more  online social networks e.g. friendster, myspace

broken out by age group

and hopefully some kind of benchmarks, like usage of email or instant messenger.

Ideally UK, but stats for any western country USA, European, maybe
even Austraila would be fine.

ideally the stats would be able to say things like:
(EXAMPLE:) out of 14-18 yr olds, XX% use social network sites, XX% use
email and XX% use instant messenger

for a bonus  5 USD , approximate usage stats in terms of hours - e.g.
teens use myspace/friendster for XX hours a week or MSN messenger for
XX hours a day

mandatories
stats must have sources and must be from 2005 or later
need to cover people ages 11(ish) through to age 20.