Although he was born in Ioannina, Kostakis began playing football in the youth system of Ajax Amsterdam at age 15.
Ajax loaned him to Dutch amateur side Stormvogels Telstar at age 19.
Soon after, Kostakis returned to Greece and joined Greek second division club Ethnikos Piraeus F.C.
[1] In July 2011, Kostakis joined the Czech Cup-winning side FK Mladá Boleslav.
[4] and in the following summer he was transferred to Greek Superleague PAS Giannina F.C.