The offences happened last week in Wakefield, when suspects phoned up their victims pretending to be police officers, then advising their victims that they need to withdraw cash.
Then the suspects have contacted the victim again to check the serial numbers on the notes.
The victim is then notes are fake and someone will attend their address to collect the money.
The first offence took place in Crofton on Monday, December 16 when on two occasions the suspect came to the house and stole thousands of pounds.
The second offence happened in the Alverthorpe area on Tuesday, December 16 when a second suspect stole thousands of pounds.
A 17-year-old man has been arrested.
He has been released under investigation.
Enquiries are ongoing to locate the other suspects.
Detective Inspector Phil Davis of Wakefield CID said: “Police officers would never ask you to withdraw money from a bank. If you received a visit from someone purporting to be a police officer, ask to see their identification card.
“All police officers whether in uniform or not carry identification. You can always phone 101 to check the officer’s credentials.
“We would ask residents to be vigilant, challenge anyone who comes without an appointment to your home.
“Please ensure this advice is passed onto elderly relatives they may care for and to look out for elderly neighbours. Please also report any suspicious incidents to the Police immediately.
“Fraud is a crime, if you have been a victim of fraud you should contact Action Fraud on 0300 123 2040.”