Michael Karg has abruptly departed as chief executive of Ebiquity with immediate effect.
The former Razorfish executive has run Ebiquity, a London-listed media auditing and measurement company, since the start of 2016.
His exit appears to have been a surprise, since Ebiquity had been due to present to shareholders at a capital markets days on 19 November. It has since called off the event.
Karg has been unable to revive Ebiquity’s share price during his tenure as the media sector has undergone rapid change.
Rob Woodward, former chief executive of Scottish broadcaster STV, has been chairman of Ebiquity since May 2018.
He said: "I would like to thank Michael for his significant contribution to Ebiquity over the past four years.
"Michael has transitioned the business towards becoming a more streamlined consultancy aligned to the demands of the evolving marketing and media environment and with a stronger balance sheet. We wish him well for the future."
Karg said it had been "a great privilege and honour" to run Ebiquity.
He will remain an employee until the year end and chief financial officer Alan Newman has been appointed interim chief executive as the company searches for a permanent successor.
Ebiquity has been on the front line of the transatlantic debate about media buying transparency in recent years, after advising the US Association of National Advertisers on an investigation in 2016 that found "non-transparent" practices were "pervasive" in media agencies.
Ebiquity’s contract compliance arm, FirmDecisions, also clashed with WPP in a high court dispute in the UK, but the two sides resolved their dispute in 2017 without a trial.