Huntingford, who will lead the recruitment process for his replacement, joined Creston six years ago and took up his current role in 2014.
Creston said the board wished to thank Huntingford for his contribution to the group, in particular helping to implement a new five-year strategy.
It was not announced whether Huntingford is seeking a new role.
Huntingford was chief executive of Chrysalis Group for seven years from 2000 and joined the company in 1987 as corporate development director, where he was principally responsible for building its radio division.
Creston also announced that Iain Ferguson would join the board immediately as a non-executive director.
Ferguson was previously a member of the executive committee at Havas SA.
Huntingford and Ferguson's roles were on the group's PLC board, which is responsible to shareholders for the group's strategy, financial and operating performance. The group's executive board is responsible for day-to-day operations, and reports to the PLC board.
In December Catherine Warne, chief executive of Health Unlimited, stepped down from her role after 10 years with the firm and in June Andrew Dougal, another long-serving member of the board, stepped down as a non-executive director.