Riding high on $17million of funding, web content discovery engine StumbleUpon has launched a new & improved advertising platform aimed to attract bigger brands to its services.

The new ad model, dubbed as a “social media brand advertising program,” is essentially an extension of its existing model, with a new pricing plan and advanced analytics tools.

The Paid Discovery tiered pricing structure ranges from “Light”, which offers basic reporting and targeting, through to “Standard”, with a top package, “Premium” offering users more advanced features.

The Premium package offers advanced targeting, guarantees a top-spot in users’ streams and also only charges for the visitors that actually ‘engage’ on the site or view a page for a certain amount of time.

The advanced targeting also allows advertisers to target users based on gender, age, location and over 500 different interest topics.

Another big development with Paid Discovery is the ability to display ads on mobile devices – allowing advertisers to reach the millions of previously un-tapped users ‘stumbling’ on their smart-phones or tablets.

How often and where the paid content is shown in users’ streams is determined by the ratings that the sponsored sites receive from the StumbleUpon community. Just like standard, un-paid content.

The new Paid Discovery ad platform clearly has its sights set on bigger investors, whereas the old model was very much targeted at smaller publishers wanting to increase traffic.

StumbleUpon has grown at a staggering rate since it was bought from eBay in early 2009, with the site now receiving over 700 million ‘stumbles’ a month from over 14 million registered users.

Paid Discovery is all part of StumbleUpon’s long-term growth plan, which at the moment, seems to be going very nicely.