South Korean police have arrested 215 people on suspicion of stealing 320bn won ($228.4m) in the biggest cryptocurrency investment scam in the country.

Gyeonggi Nambu provincial police said on Wednesday that the arrests included the alleged mastermind of the organised crime group accused of selling 28 types of virtual tokens to about 15,000 people by promising high returns. Referred to as Mr A, he had fled to Australia but was arrested and extradited. Police have confiscated 22 bitcoins from his accounts and have applied to seize some $34m more. Just 12 people of the 215 remain in custody, according to Yonhap.

Police said the group had issued six of the 28 tokens on overseas crypto exchanges and were managing a team of market makers to push up prices. Police described the tokens as “worthless”. Members of the alleged criminal ring are also accused of using personal information garnered through both digital advertising, including nearly 9m phone numbers, and theft to take out fraudulent loans.

The group had set up investment consulting companies and sales teams to sell the virtual assets to people who had subscribed to a YouTube channel that had accrued hundreds of thousands of subscribers, the police statement said. They allegedly preyed on middle-aged and elderly victims.