"I hope to be able to repay the fans [for their support]," Reina told reporters.
"The welcome I have received from the beginning was wonderful. Naples is a wonderful city. I was impressed when I saw Stadio San Paolo for the first time.
"This team has to grow and only think about going one game at a time. The dressing room knows that we'll have to work hard to win. I have always said that the best coach I have worked with was [Napoli boss] Rafael Benitez."
Reina made 396 appearances for Liverpool.