The German goalkeeper has joined Besiktas on a two-season loan.
Along with a picture of his holding a Besiktas shirt, he tweeted: "Proud to be part of the famous Besiktas family now. Your welcome at the airport yesterday was simply overwhelming! I will give it my all to win with Beşiktaş.
"A big Thank You goes out to all of the Liverpool fans for the support until now – you indeed never let me walk alone."