The audacity and creativity of a pickpocket gang who worked shifts, employed teams of runners and made tourists their exclusive prey has been revealed by one of the most successful crackdowns to date on street crime in Greece.

Pickpocketing may flourish in tourist havens, but in Athens, where visitor numbers are booming, thieves appear to have been on a roll. With takings in excess of €3,500 (£3,100) a day, pickpockets posing as holidaymakers built a criminal network of unprecedented scale, “working” the public transport system for the best part of a decade.

Nikos Toskas, the alternate minister of public order and citizen protection, told the Guardian: “Police are telling us that since the arrests, there have been much fewer cases on metro, train and bus lines. This has long been a problem and we have taken a big step forward in tackling it.”

In a recent operation, police rounded up 31 gang members in early morning raids at properties in Athens and the port city of Piraeus. Christos Papazafeiris, the head of security police for the greater Athens region, said: “They had built up such a structure and developed such skills that every day they could carry out at least 15 thefts.”

Tourists heading to and from Athens airport on the metro were their favourite targets, along with older people and those with mobility issues. CCTV footage and witness testimony revealed the gang working in small groups using props including newspapers and maps as decoys. At least three people would distract a victim before another gang member did the pickpocketing, passing the goods to someone else in what police described as a highly effective relay.

A second division of runners and scouts were paid for from the profits, with each group providing cover for the other. “Many months of systematic and specialised police work were required to achieve these important results and dismantling of the criminal network,” Papazafeiris said.

Foreign visitor numbers are expected to top 5 million, more than the Athens urban area population, by December. Profiting from the drop in the number of tourists heading to Egypt and Turkey, Greece is expecting an unprecedented 30 million tourists in 2017.

Ioanna Rotziokou, a Greek police spokeswoman, said: “In terms of street crime, this operation has been a great success. These people were so successful that during the summer, they expanded to other tourist areas in Greece, including popular islands in the Cyclades.”

A total of €9,500 was found in 498 wallets confiscated by police in the raids, but more than 4,000 cases of theft are believed to have occurred during a 10-year period, with takings in the hundreds of thousands of euros.

The culprits, who used false identities to acquire mobile phones and tip each other off, ensured they blended in with passengers by wearing sports and casual clothes.

Police believe 18 gang members are still at large. Most of those arrested, including a woman thought to be the gang’s leader, were from Albania. A former Greek police officer, who played a key role providing protection, was also among those arrested.

“They worked with mobile phones; they tipped each other off. Police protection meant they could keep away from areas that were guarded,” said Rotziokou.

The operation has led to the resolution of 764 reported thefts of wallets, mobile phones, tablets and other valuables, but police say most of the stolen goods have since been sold or taken to Albania. Stolen foreign currency would be exchanged into euros at bureaux in Athens.

Although Greece is known for its safety, pickpocketing has long been seen as a major problem for holidaymakers. Travel guides address it, with some advising tourists to use decoy wallets and fake credit cards. In a blog dedicated to defeating pickpockets, Matt Barrett of Athensguide.com told how a Greek-American woman caught one culprit by placing a mousetrap in her purse.

With the country’s struggling economy more dependent than ever on tourism, and one in five people working in the sector, officials are taking crime seriously. Toskas said security had been upgraded and Greek police were receiving training from their British counterparts in on-the-ground policing and signal intelligence.

“We have 52,000 police nationwide and 16,000 in Athens, and have increased patrols in tourist areas dramatically,” the minister said. “The UK has very good city policing, very good intelligence services and we have been cooperating very closely with them on both.

“Street crime and pickpocketing are linked to the crisis that has hit our country and just as we have done with bank heists and supermarket robberies, we are determined to deal with it once and for all.”