Chuku, part of the team that launched Element a year ago, is creating an agency called Staufenberger & Smith & Butt with the former ZenithOptimedia planner Patrick Syms.
Element, which recently lost the BMW and Mini media planning business to PHD Group, will continue to work on clients such as 118 118 without Chuku, who previously ran the 118 118 business as a planner at Naked.
Chuku is the second key figure to depart from Naked's joint ventures.
In September, Philip Dowgierd quit as the head of its partnership with Fallon, Happen@Fallon. He is now the strategy director of the digital shop Greenroom.
Chuku said the start-up, which takes its name from obscure figures outside advertising who have inspired Chuku and Syms, will give communications planning a new twist.
"Everybody who claims to do communications planning comes at it from a media perspective. For us it will be about coming at it from an account planning perspective, deciding which channels to use but also the nature of communications," he said.