Last June, pop star Delta Goodrem serenaded the diamond-dealing playboy as he celebrated his 30th birthday at St Kilda East venue Red Scooter.

Photographs of him quaffing Dom Perignon on his regular first-class flights to Europe were flaunted on social media with the hashtag "PoorGuysSuck".

In just six years, Mr Mendieta transformed his business Gold Buyers Melbourne into a multimillion-dollar empire that turned over $66 million in the 2015-16 financial year, according to records obtained by Fairfax Media.

But the good times hit a roadblock on Thursday morning when detectives from the gangs crime squad stormed his Collins Street offices, where gold and precious stones are traded.

The raid was part of a major police investigation into the alleged fencing of jewellery stolen in a series of armed robberies on jewellers and private homes across Melbourne over the past year.

Police also raided Mr Mendieta's penthouse residence in Roy Street, just off St Kilda Road, where they impounded a Lamborghini Gallardo, and other luxury properties in Southbank and Caulfield North.

Mr Mendieta was one of three Colombian men arrested. As yet, no charges have been laid.

A police spokesman confirmed officers had seized items believed to either be stolen or the proceeds of crime, including cash, gold, precious stones, silver and gold bullion.

"The investigation into the selling and receiving of stolen jewellery was launched by the gangs crime squad following a series of jewellery store armed robberies across Melbourne over the past year," the spokesman said.

The robberies are understood to have included broad daylight attacks on suburban jewellery stores involving gangs of youths armed with machetes, baseball bats and hammers.

Even as detectives gathered evidence at Mr Mendieta's offices on Thursday afternoon, suspected criminals continued to alight on the 11th floor with gems and precious metals to sell.

Police arrested a 16-year-old with a plastic bag containing assorted jewellery including an antique fob watch and gold knuckle-dusters.

Owners of other businesses in the building complained that "unsavoury types" including members of outlaw motorcycle gangs regularly visited the offices of Gold Buyers Melbourne.

At least one business recently relocated because of the dubious clientele.

Crime Command acting commander Peter De Santo said Thursday's arrests and seizures highlighted the scope of these criminal enterprises.

"It's not only about identifying and targeting offenders involved in violent incidents at jewellery stores; it's also about investigating what happens after those offences occur," Mr De Santo said.

"We know that offenders will be looking to move on items, many of which have significant value, so it's about making sure we follow those lines of inquiry and stop those providing avenues for the disposal of these goods.

"These incidents have a significant impact on victims, whether it's those who are in the store at the time of the offence or those business owners who are left with the loss of stock and damage to their stores," Mr De Santo said.

Mr Mendieta appeared unfazed by the police attention on Thursday, repeatedly smiling at a Fairfax photographer.

The 31-year-old founded his business in 2011 with older brother Julio Mendieta, who was also born in the Colombian city of Bucaramanga???. Another brother is involved in the jewellery business in Adelaide.

Aside from trading gold and gems, Mr Mendieta also offers high-interest loans that are usually secured against expensive jewellery.

In 2016, he lent more than $1.1 million to third parties, including bankrupt diamond trader Ronnie Bensimon, who amassed debts of more than $10 million.

Mr Bensimon is being pursued in court for 12 diamonds, some of which were used as collateral for short-term loans from Mr Mendieta, who charged interest of up to 48 per cent a year.

Mr Mendieta is just weeks away from settling on a $2.5 million property in Surrey Hills, and recently bought a development site in Dandenong for $1 million.