Charles Miller has had his media diet reshaped by social networks.
Just a year ago, the marketing executive for DirecTV in Los Angeles began his day by looking at the home page of the Yahoo website, surfing links to the major news stories selected by the site's editors. But today Mr Miller begins his day on Twitter and Facebook - primarily social networking sites - where he reads stories and watches videos suggested by his friends and connections.

Mr Miller's changing habits are representative of a broad shift occurring among internet users.

With social media on the rise, traditional internet portals such as Yahoo and AOL, once the front doors to the online world, are being spurned in favour of social sites, where users are discovering a new, more personal filter to the infinite world of the internet.

"The people you know are going to pick things that are more interesting to you," says Mr Miller.

This behavioural change has forced content providers to adapt quickly. Rather than assuming that users will seek out their content, media organisations - from the big international newspaper groups, down to the small local publications - are now actively promoting their content on social networks, and encouraging readers to distribute links to their friends. It is de rigueur for news websites to be embedded with devices that automatically publish articles to social networks such as Facebook and Twitter and to content sharing websites such as Digg and StumbleUpon.

"We need to be where people are talking about our content and consuming our content," says Jennifer Preston, social media editor for The New York Times. "It's very old fashioned to think that your readers will consume all of the content on your site and just come to you."

The New York Times has aggressively promoted its content on social sites. Its main Twitter account has more than 1.7m followers, its Facebook page has more than 460,000 fans, and it has set up Twitter accounts for all its various blogs.

Precise statistics about the rise of sharing information through social networks are hard to come by because links are being shared on multiple platforms, and new services such as link-shorteners are complicating efforts to monitor the flow of traffic. Link shorteners reduce a typical URL, or web address, which can extend to hundreds of characters, so they are easier to copy and paste.

But the broad strokes are clear. Media companies' efforts, coupled with the increase of sharing online, have effectively turned social networks into massive engines of recommendation, responsible for directing an ever larger amount of online traffic.

On Facebook, the number of links shared has doubled in the past four months, jumping from 9m in April to 18m in August. Links on Facebook are now responsible for 19 per cent of visits to Huffington Post, the US news blog, and are also the number one driver of traffic to the Perez Hilton gossip website.

This is a potential boon for media companies, who are always seeking to broaden their audience. Online readership on most major content sites is up. "The media organisations have responded quickly to accommodate people who are sharing," said Bill Wasik, an editor at Harper's magazine and the author of And Then There's This: How Stories Live and Die in Viral Culture . "The big organisations are doing a good job of that."

But while news organisations and content providers are enabling sharing across multiple platforms, it is not yet clear how these 'engines of recommendation' are shaping what news is most read. Early indications suggest that while social media may be directing more eyeballs to news sites, it is upending traditional editorial agendas.