Brighton-based Spannerworks was founded in 1997 and has developed the digital presence of Best Western Hotels, confused.com, SN Brussels Airlines and Kiddicare. It is currently working on online campaigns for BT and HBOS.
ICrossing has been looking for acquisitions since it hired Don Scales, former chief executive of Agency.com, in May 2006, as chief operating officer to work alongside Jeff Herzog, founder and CEO. In December 2006, the company acquired US search agency Newgate Internet and the deal to buy Spannerworks is set to be followed by further acquisitions.
The purchase will give iCrossing its first office outside the US and marks a significant venture into the European market. The company currently has offices in Atlanta, Chicago, New York, Dallas, San Francisco, and Arizona.
Spannerworks, which will retain its name, is headed up by Arjo Ghosh, chief executive, who owned the vast majority of the company and will continue to head it up.
Although there is no confirmation of the price paid, Ghosh has said it is "in excess" of the £9.2m ($18m) being quoted by some sources.
Ghosh said: "We set out to partner with a company that understood search and its importance in digital marketing, with a range of products and services to complement our own.
"iCrossing is the perfect match, and this deal squarely puts Spannerworks ahead of the market. From this month forward, we will be embarking on a global expansion strategy in partnership with iCrossing and will be keenly hunting for the best European talent in the industry."
Herzog said: "The strengths of both companies will be leveraged in the US and Europe to deliver to our clients unmatched global media strategies in the digital space."
At the same time, Spannerworks has announced immediate expansion into London and further acquisition ambitions including Europe.