The arrival of Son, from Young & Rubicam Europe, reflects Initiative's desire to build its planning strength by developing a link between account and media planning.
Son will provide European leadership on key accounts' strategic direction.
Her priority is to supervise European communication planning teams, including Unilever's, to deliver an improved service as part of Initiative's "expect more" positioning.
Part of Son's role is to work with the heads of communications planning in each market, including Tony Manwaring in the UK, on delivering higher levels of strategic output.
She will offer leadership in recruitment and development of people, evolving Initiative's planning product, working with Initiative's research experts, collaboration with other agencies and on the planning side of new business.
Son has worked in advertising agencies, brand consultancies and on the client side. She worked in planning while at FHV/BBDO in The Netherlands before roles in international marketing at Unilever, Revlon and Gillette.
Mike Tunnicliffe, Initiative's executive vice-president and the worldwide account director on the Unilever business, said: "We needed someone with a very different background compared with traditional media - someone to give our planners a different perspective."