The German goalkeeper has signed from Liverpool on a two-season loan.
At his presentation, Karius declared: "I am a young age for a goalkeeper, my goal here is to win cups with my teammates, to earn the victories. The fans are exciting here, Beşiktaş will contribute to my development.
"The support of the fans was extraordinary, I feel very good, I feel the support of fans so much, it is a unique support.
"The biggest reason I came here is the messages the fans sent me ... they showed me what they really wanted ... Every player wants to feel such love ... you want to do the best with this feeling.
"I spoke to the German players who played here, they were totally positive.
"I have not spoken directly with Mario Gomez, but I've heard absolutely positive things, I know what he's doing here, and I've heard absolutely positive things from our teammates."