Real-time advertising firm AppNexus has appointed Jonathan Hsu – previously CEO of 24/7 Media, a tech company which sold to WPP for $649m in 2007 (£391m) – as its CFO and COO.

“At 24/7 Media, Jon built and sold one of the biggest ad tech companies ever,” said Brian OKelley, CEO and co-founder of AppNexus. “Hes an extraordinary talent and true industry pioneer with unique, proven experience as CEO, CFO and COO of a digital marketing business – a background that will be invaluable as we cement our place as an elite, global technology company.”

Hsu is one of four appointments being announced by AppNexus. Geir Magnusson Jr will join the company as CTO; Casey Birtwell has been hired as SVP, strategy & operations; and Michelle Dvorkin will take a new role as SVP of people, responsible for all aspects of HR.

Last year, AppNexus doubled its headcount with the hiring of more than 300 new staff and landed $75m in Series D funding.