Martin (Flynn) Cawood, Cody Lynch-Stuart and Noah Read — all aged 15 — were last seen in their home city of Wodonga, on the border with NSW — last Wednesday.
In a statement, Victoria Police says its investigators believe the boys may have been travelling together and may be in Melbourne — more than 300km away from their hometown.
Their families are concerned for their welfare due to the length of time they have been missing.
Investigators have released photos of the boys as part of a public appeal to find them.
Anyone with information on their whereabouts should call Wodonga police station on (02) 6049 2755.
38,000 Aussies are reported missing every year1:24
Although most people reported missing are found alive and well, there remains around 2000 missing long-term.