Lawson is promoted from global chief client officer.
Moves follow departures of Sue Higgs and Caroline Pay.
Spending related to the US election shored up ad revenue for YouTube which grew by 14% globally.
Toby Southgate had left Forsman & Bodenfors last October as global chief executive.
Facebook chief Mark Zuckerberg’s decision to move to a community-based moderation system leaves marketers questioning whether they can, or should, trust Meta.
Kalifa departs after two years with the company.
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