Sorrell's S4 Capital bolsters board with Colin Day appointment

LONDON (Reuters) - S4 Capital, the digital advertising group that has lost 80% of its stock market value this year, has appointed British business veteran Colin Day to its board to help oversee its audit and risk requirements.

The company, built by Martin Sorrell, cut its earnings outlook last month due to surging costs, and was forced to delay the publication of results earlier this year when the auditor said it was not ready to release them.

It said on Tuesday it would appoint Day as a non-executive director. He has previously sat on boards including Reckitt Benckiser, Sorrell's former group WPP, Cadbury, Imperial Brands and easyJet.

S4 also appointed Chris Martin, a co-founder of MightyHive, as its chief operating officer.

(Reporting by Kate Holton. Editing by Andrew MacAskill)