WPP Plc. cut its outlook for 2025 after clients spent less than expected, adding to the advertising agency’s woes as it searches for a new chief executive officer. Shares fell to their lowest level in almost 16 years.

British ad group WPP slashed its profit guidance after some big clients left, others cut spending and new business dried up in June, putting it further behind Publicis in an industry navigating the impacts of AI and economic uncertainty.