There have been a spate of smash-and-grab-style robberies since October in the city's most prestigious suburbs – including one Toorak jeweller who has been robbed twice - that has terrified employees and led to crisis talks with senior police.

Victoria Police Assistant Commissioner Rick Nugent said the latest armed robbery was particularly violent, brazen and cowardly.

But he vowed a new taskforce, called Operation Fuller, would not rest until all the robbers were caught.

"What the community expects is that we'll do it thoroughly, and meticulously, to gather the evidence we need to get a successful prosecution in court - and that's exactly what we're doing," he said.

"They can have absolute confidence that we're doing every single thing we can to apprehend them."

It had been Elaine Frankie-French's first day back at the IMP Toorak jewellery shop from stress leave since she had a gun held to her head when the store was robbed by who she believes to be the same gang who targeted the store on October 25.

"Four guys ran in the shop, they smashed as they went," she said.

Police are still searching for four men of African appearance who entered the store just before 1pm.

A separate attack on Holloway Diamonds in Canterbury Road, Canterbury, last week was in broad daylight when young offenders wearing masks took off with a "large quantity" of jewellery.

One teenager appeared at the Melbourne Magistrates Court on Friday in relation to that robbery, with a second set to face the Childrens Court.

"We can assure the community that recent incidents in Toorak and Canterbury are the subject to thorough ongoing investigations," police said in a statement.

Mr Nugent said the Apex gang is not believed to be involved in the jewellery store crime spree.

Instead, he said eight jewellery store robberies may be connected to a loose group of teenagers, some who are being recruited through social media.

"Particularly with social media, we see a lot more people who connect through that, and who might be available to commit a crime at a particular time," he said.

The taskforce is also examining if the teenagers are being directed by larger organised crime groups, who have the resources to then sell the jewellery, he said.

He would not reveal if police have so far uncovered any evidence of links to established crime groups.

The Jewellers Association will meet with senior police on January 24 in a bid to bring an end to the crime wave.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000.

The eight robberies the taskforce believes may be linked are:

​1. Reservoir, 2/7/16

2. Coburg, 7/7/16

3. Toorak, 25/10/16

4. North Melbourne, 26/10/16

5. Lalor, 14/11/16

6. Lalor, 4/1/17

7. Canterbury, 12/1/17

8. Toorak, 14/1/17

- with Daniella Miletic, Goya Dmytryshchak