The 31-year-old made more than 140 appearances for the Magpies after joining from Bordeaux in 2013, scoring 19 goals.
Seven of those came during the 2016/17 campaign, with the Frenchman a regular as United bounced back to the Premier League at the first attempt.
His new club, Göztepe – based in the city of ĺzmir – have just returned to the Turkish top flight for the first time in more than a decade.
Newcastle United would like to wish Yoan the best of luck for the future.