A couple of weeks ago, a teenager shocked the world by announcing that teens don't use Twitter. This passing remark in that now famous Morgan Stanley research note - which detailed the views of 15-year-old intern Matthew Robson on media and modern devices - set the London media and Twitter alight.

The general response was: 'What does this kid know? How can he be representative of all teenagers?'

The truth is, he probably isn't and it doesn't matter because we already knew that most teenagers aren't that switched on to Twitter.

So who is using it - and how can you get their attention?

As businesses get savvy about using microblogging, knowing who they can reach with which service becomes ever more important.

Tweeting teens 
First let's look at whether Robson could be right. Are teens turned off by Twitter?

First glance at figures from Sysomos, which analysed Twitter usage of 11.5 million subscribers in May 2009 found that 31 per cent of users that disclosed their ages were 15 to 19 years old, and 35 per cent were between 20 and 24.

However, Sysomos cautions that only 0.7 per cent of users disclosed their age, with younger users showing a higher probability of doing so, so these figures could be misleading.

Other surveys and analysis imply that average users are indeed a lot older than the Sysomos study suggests. ComScore, which tracks internet activity, estimates that the majority of Twitter's users are over 35, and a survey by Pew Internet & American Life Project of US adult Twitter users found that the mean age is 31. This compares to 26 for Facebook and 27 for MySpace.

Further evidence that Generation Y is not switched on to microblogging: Participatory Marketing Network (PMN) found that of 200 young adults surveyed, 99 per cent had profiles on sites like Facebook and MySpace, but less than a quarter had Twitter profiles.

This may be skewed by the sheer size of Facebook (200 million) compared to Twitter (about 20 times smaller). Or could it also be because Facebook allows you to control who is in your circle, while Twitter is an open discussion with anyone who wants to listen? Most teenagers want to chat with friends, possibly make new ones but certainly not have adults listening in.

So who is using Twitter? 
Whatever the mean age of users, Twitter does appear to be the social media of choice for the older crowd. It could be that more of the population is over 25 than younger than it, or that many of the 40-year-olds have been using the internet for 10 or 15 years and so are quite familiar adopting new forms of communications.

It could also be that they occupy the professions most likely to be using it regularly: advertising, marketing, journalism, media experts.

Take a look at the Sysomos' Twitter usage statistics: Just five per cent of Twitter users account for 75 per cent of all activity. These very active people are often self-publicists: 15 per cent of Twitter users following more than 2,000 people describe themselves as social media professionals. A third of social-media professionals will post every single day.

Most Twitter users are much less active: more than 90 per cent of users have less than 100 followers and follow less than 100 people. One in five who has registered has never posted at all.

So what can we learn from this? Apart from a handful of big personalities such as Ashton Kutcher (@aplusk) and Stephen Fry (@stephenfry) or brands like Dell (@DellOutlet) and US budget airline JetBlue (@JetBlue), most people's followers and friends on Twitter are in proportion, and those that are most active in following and tweeting get the most friends.

Building a following 
So how do you tap into this crowd of opinion formers and build a following? Take this advice from Kevin Hillstrom, who data-mined his own list of followers. He found that:

• For every 100 individuals you follow on Twitter, you'll earn 79 followers.
• For every 100 updates you have on Twitter, you'll earn 16 followers.
• Each additional follower you earn tends to have fewer and fewer followers... to be expected as a social media tool grows in popularity.

This will explain why, if you have tried Twitter only briefly and wondered why power users (those with 1,000s of followers) have signed up to follow you, it is not because you necessarily have anything interesting to say, it's simply a numbers game.

Your followers will look at your other followers and follow them, attracted to those with most followers of their own. Following is the best way to generate new followers.

So does that mean 'following' is an end in itself? Of course not, but when the Twitterverse is increasingly being drowned in the noise of millions of people liveblogging their lunches, the larger your base, the more chance that when you do actually have something to shout about, there will be someone listening.

This article first appeared on Silicon.com