ISTANBUL (Reuters) -Turkish police have detained 62 people in an investigation of a cryptocurrency trading platform provider, state-owned Anadolu news agency said on Friday, after thousands of Turks filed criminal complaints saying they had been scammed.

The Thodex cryptocurrency trading platform, which had been handling daily cryptocurrency trade worth hundreds of millions of dollars, said on its website on Thursday it would be closed for four to five days due to a sale process.

But users who have not been able to withdraw money or access their accounts voiced concern on Twitter that they may have been defrauded, comments widely picked up by Turkish media.

Prosecutors issued arrest warrants for 78 people and 62 had so far been detained in an operation centred on Istanbul but stretching across eight provinces, Anadolu said.

Istanbul police said the company’s founder and CEO, Faruk Fatih Ozer, had flown to the Albanian capital Tirana on Tuesday.

Anadolu said on Friday Turkey’s Justice Ministry had launched the process of seeking Ozer through a wanted person “red notice” and calling for his extradition from Albania.

An Istanbul prosecutor’s office on Thursday said it launched an investigation into Thodex due to claims that the platform had led to the “aggrievedness of many citizens”. Turkey’s financial crimes investigation board MASAK blocked the company’s accounts on Wednesday and began an investigation, a MASAK source said.

Thodex said “negative” media reports about it were untrue, and that banks and funds – which it would identify later – wanted to invest in the company and had proposed a partnership.

The 24-hour trading volume on Thodex was $538 million on its last trading day, according to Coinmarketcap.

Last week Turkey banned the use of crypto assets for payments, adding to factors that sent bitcoin down 14% at the weekend. Turkey’s central bank cited “irreparable” damage and transaction risks as reasons for the ban.

(Reporting by Daren Butler; Editing by Nick Macfie)