The husband-and-wife team founded Dunnhumby, the customer insight business, in 1989.
They pioneered the use of data analysis for customer benefit and signed their landmark deal with Tesco in 1994, later selling the business to the supermarket giant for £93m.
Dunn and Humby have now joined the board of Starcount as executive directors and taken a "significant minority equity stake" in the business, which aggregates data and trends across the world's 11 most popular social media networks. Starcount has acquired the pair's new H&D Ventures business as part of the deal.
Dunn said: "Social media has thrown up an intriguing new hypothesis for data analysts – that networks are to a very significant extent driven and influenced by a very small pool of users, in a way that could never have been possible before the internet.
"This creates huge opportunities for both brands and their customers – to create a social loyalty currency which will allow companies to properly understand and engage their digital audience."
She said Starcount dealt with trends across all the major social platforms, putting it in a stronger position to help brands understand their entire digital audience than the likes of Facebook or Twitter could do on their own.
Dunn said: "Even Facebook or Twitter only understand the users in their network.
"We strongly believe that social media offers the base to create more targeted and user-friendly loyalty relationships, and look forward to exploring this hypothesis with Starcount."
Starcount is also in the process of finalising a third equity fundraising of $5m (£3.25m) with investors Artemis, Praetura Capital and Christopher Carter, former vice chairman of institutional securities and now senior adviser at Morgan Stanley, who becomes chairman.
Drew Thomson, group chief executive, said: "Reaching the right audience is the core focus of any brand or star. Starcount is about unlocking the potential of social media to show brands and stars the secrets of their success, and identify the real influencers.
"With the world-class experience of Edwina Dunn, Clive Humby and Christopher Carter, we are aiming to change the rules of social engagement, and make sense of the billions of new fans social media has created."
Starcount publishes daily charts of the world's most popular brands and stars, as well as their biggest fans, based on analysis of 1.7 billion social media users' activity across 11 networks, including: Facebook, Twitter, Google+, YouTube, Sina, Tencent, Youku, Renren, Mixi, Orkut and Vkontakte.