The cyber criminals have expanded from targeting people in Asia to include people in the US and Europe.
The team from cyber security firm Sophos uncovered a Bitcoin wallet controlled by the attackers that contains nearly $1.4 million in cryptocurrency, allegedly collected from victims.
Sophos researchers have code-named the threat "CryptoRom" which relies heavily on social engineering at almost every stage.
First, the attackers post convincing fake profiles on legitimate dating sites.
"Once they've made contact with a target, the attackers suggest continuing the conversation on a messaging platform. They then try to persuade the target to install and invest in a fake cryptocurrency trading app," said Jagadeesh Chandraiah, senior threat researcher at Sophos.
"Our research shows that the attackers are making millions of dollars with this scam," he said in a statement.
In addition to stealing money, the attackers can also gain access to victims' iPhones.
In such attacks, cybercriminals leverage "Enterprise Signature," a system for software developers that helps organisations to pre-test new iOS applications with selected iPhone users before they submit them to the official App Store for review and approval.
"With the functionality of the 'Enterprise Signature' system, attackers can target larger groups of iPhone users with their fake crypto-trading apps and gain remote management control over their devices," the report claimed.
This means the attackers could potentially do more than just steal cryptocurrency investments from victims. They could also, for instance, collect personal data, add and remove accounts, and install and manage apps for other malicious purposes.
Until recently, the criminal operators mainly distributed the fake crypto apps through fake websites that resemble a trusted bank or the Apple App Store.
"The addition of the iOS enterprise developer system introduces further risk for victims because they could be handing the attackers the rights to their device and the ability to steal their personal data," Chandraiah warned.
To avoid falling victim to these types of scams, iPhone users should only install apps from Apple's App Store, the researchers suggested.