BSkyB has invested £4.3 million into an American online sports firm targeting the hard-to-attract market of young 'millennial' viewers.

The pay TV giant - with over 20 million customers in the UK, Italy and Germany - said it has signed a deal with New York-based Whistle Sports to create videos for fans in the 16-to-34 age group based around celebrities and sports such as basketball, baseball, football, and American football.

Whistle Sports, which began its service in January, said its library of 28,000 videos are shown across 190 different new media channel partners and have been watched 1.25 billion times. It said it has 8.3 million subscribers.

The deal is the latest in a series of investments in new media start-ups by Sky in an attempt to appeal to younger audiences who watch less traditional TV.

Sky has recently signed agreements with PlutoTV, the American online video aggregator, and the US ad tech firm Sharethrough.

Whistle Sports said it also has relationships with young sports stars such as NBA player Jeremy Lin and Ultimate Frisbee champion Brodie Smith, who have million of followers on social media.

The US firm said it shows its videos across new media platforms such as YouTube and Xbox.

Sky Sports managing director Barney Francis said: "Whistle Sports has very quickly established itself in the US as a major new sports network. We see lots of potential to harness Sky Sports' content and relationships with major sports bodies and brands to work alongside Whistle Sports' talent network."

He added that the companies planned to work on content that would appeal to younger audiences.

Whistle Sports founder and chief executive John West said: "This partnership is a tremendous fit for us, given our focus on international expansion."

"Sky is a recognised leader in sports entertainment and delivery and brings to the partnership some of the highest quality creative and production teams in sports."

Sky holds broadcast rights for Premier League football, Formula 1, international cricket, international rugby and European and US golf.