Drogba was outstanding in the closing weeks of the season as Chelsea won an FA Cup and Champions League Double.
Luiz told the People: "Chelsea are obliged to fight for the Premier League title in the next campaign. This is our challenge and obligation.
"For me, it is a pain that Didier Drogba is leaving because few players in the world possess his battling spirit on the field. Didi is unique and in the final he was sensational."