The announcement of a number of new tools and apps for Twitter has come following a Pew Internet report indicating that the micro-blogging site has a growing body of younger fans flocking to it.

The study shows that 19% of internet users now say they use Twitter or another service to share updates about themselves, or to see updates about others, representing a significant increase over previous surveys in December 2008 and April 2009.

Three groups of internet users are mainly responsible for driving the growth of this activity: social network website users, those who connect to the internet via mobile devices, and younger internet users.

According to Pew Internet, users aged 18 to 44 report rapid uptake of Twitter over the last nine months, which slows after that – 37% of internet users aged 18 to 24 use Twitter or another service, up from 19% in December 2008.

From May 2008, the median age of a Twitter user is 31, for MySpace it is now 26 (down from 27) in, LinkedIn is now 39 (down from 40), with Facebook’s user median age growing to 33, up from 26.

The study follows the announcement by company founder Biz Stone that the practice of retweeting fellow users’ messages will be formally incorporated in to the site’s design, along with the ability for users to track how many times a tweet is repeated by others.

Stones said that the feature is only available on a very small percentage of accounts for now.

“The plan is to see how it goes first with this small release. If it needs more work, then well know right away. If things look good, we’ll proceed with releasing the feature in stages eventually arriving at 100%,” Stone wrote on the site’s official blog.

Also, Australian iPhone development firm Syncode released its latest version of iTweetReply, a Twitter push application featuring not only reply and DM push, but search and timeline messages pushed straight to your iDevice.

“Syncode hopes that search capability will benefit its current users and bring iTweetReply to a new market of business users, giving them the ability to be instantly alerted when people are talking about their business or slogan,” said Syncode co-founder Matthew Lesh.