Bertozzi, currently marketing and new business director, will oversee an increased focus on digital at the agency.
ZenithOptimedia chief executive Gerry Boyle said: "There has been an evolution of the way we have been approaching these channels for some time.
"This is not a radical restructure, but a move to make sure the agency is fit for purpose.
"The new role reflects the growth in the importance of digital channels at the agency and Marco, who has had years of experience in that space, is best placed to provide a focus."
Bertozzi will also work with ZenithOptimedia's sister agency Zed Media in some areas.
The agency's planning director Christian Lee will take over from Bertozzi as marketing and new business director.
Bertozzi's promotion follows rival agency Vizeum's hiring of Ross Barnes as head of search, revealed in Media Week (29 May, page 5).
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