Interpol is conducting an international search for these two teenagers, aged 15 and 16 respectively, whom are suspected of having joined the civil war in Syria, Xinhua quoted the Austrian police as saying.
"We have gone to Syria to fight for Islam. We will meet in paradise," the missing girls noted in two identical letters they left behind, police said.
Authorities believe they were tricked into travelling to Syria to fight for the rebels.
Both girls are from Bosnian families who immigrated to Austria and are believed to have flown to the Turkish city of Adana, close to the northwestern border of Syria.