When Karen's boyfriend asked for money to help move to Australia she didn't hesitate, unaware she was falling prey to a scammer who would go on to swindle her of more than $600,000.

Karen* is one of many Australians who are losing combined millions to scammers while searching for love online, with the most cash fleeced around Valentine's Day.

It has prompted a warning from the Australian Competition and Consumer Commission and ANZ, who said they conducted 119 investigations worth a total of $3.7 million during a six-month period in 2017.

Karen* is one of many Australians who are losing a combined millions of dollars to scammers while searching for love online, with the most cash fleeced around Valentine's Day (Stock image pictured)

It has prompted a warning from the Australian Competition and Consumer Commission and ANZ, who said they conducted 119 investigations worth a total of $3.7 million during a six-month period in 2017 (Stock image)

'Valentine's Day is one of the busiest times for online romance scammers,' ANZ's Catriona Noble said.

'A friend request on Facebook or a message on a dating site from a stranger might be the start of a romance scam, so it's absolutely vital to recognise the signs.'

A report by ANZ reveals Australians over the age of 55 are the most vulnerable, with men more likely to be the target of romance scams, although women stay involved with their scammers for longer, losing more money as a consequence.

Online con artists often go to extreme lengths to create realistic profiles and groom their victims over weeks, months or years to build a relationship - a practice commonly known as 'catfishing', the bank says.

Once they have gained their victim's trust, they start asking for money for a range of emotive reasons.

Online con artists often go to extreme lengths to create realistic profiles and groom their victims over weeks, months or years to build a relationship - a practice commonly known as 'catfishing', the bank says (Stock image)

In another example, a man exhausted his savings to help a woman he met online who claimed to be in trouble with people to whom she owed money.

After building a close rapport with the woman by chatting online for more than a year, he sent $200,000 and awaited her arrival in Australia.

The man went to the airport on multiple occasions to pick the woman up, but she never arrived.

*Karen is not her real name.