Six bandits brandishing a box-cutter robbed four people across three suburbs in less than four hours, police believe.
Greater Dandenong CIU detectives are investigating the Saturday 19 August incidents.
The first occurred about 7.50pm, when six men approached a man walking along Foster Street, Dandenong.
Police said the group assaulted the victim and stole his wallet, leaving him with a large gash to the side of his head.
About 10 minutes later in the same area, six men approached another man and demanded his wallet before assaulting him and stealing his phone.
In James Street, Springvale, about 8.10pm, five to six men approached a man and one produced a box-cutter.
They assaulted him and stole his phone and wallet.
The fourth incident occurred in Joy Street, Noble Park, about 11.25pm.
Two men approached a man and knocked the victim to the ground, held him down, assaulted him and stole his wallet.
Police said the victims described their attackers as African in appearance.
No-one was seriously injured during the incidents.
Investigators believe the string of robberies and attacks might be linked.
They urged anyone with information to call Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au.
