Police allege 197 merino ewes with purple ear tags and 493 white Suffolk merino cross lambs with red ear tags were herded from a farm at Logan between October 21 last year and February 1.
The missing merinos are valued at about $139,000 and were in full wool at the time of the alleged theft.
Investigators say the stock may have been transported interstate and the alleged offenders would have needed to use at least two four-decker trucks.
They also would have needed to use a significant amount of portable fencing, as well as sheep dogs to round up the livestock.
The owners did not notice the sheep were missing until this month.
"It's been very well planned, I would say," Leading Senior Constable Dan O'Bree told ABC Radio Melbourne on Thursday.
"If 700 sheep have got out, the neighbours would have let the victim know. If 700 sheep died in his paddock, he would have known."
Police believe the alleged thieves could have sold the wool, or taken off the ear tags to sell the animals.
"We'll keep digging around," Sen Const O'Bree said.
"Hopefully someone can come forward with a bit of info that might be able to help us with something."
Anyone with information is urged to contact Crime Stoppers.
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