Wales Air Ambulance discovered the scam over the weekend. He says he is campaigning to get social media companies to fix fraudsters.
A spokesman for the charity, which has a base at Welshpool Airfield, said on Friday it had run a competition with a chance to win a VIP trip to one of its bases.
“Unfortunately, over the weekend, one or more scammers created fake Instagram and Facebook accounts in the name of our charity.
“They were using the contest to obtain personal and financial information from our supporters. Their intentions were fraudulent.”
The charity urged its followers not to click on any links associated with fake accounts that asked people to register their details.
“For the safety of our supporters, we have decided to cancel the competition. We hope this will further help members of the public distinguish between our accounts and protect them from fraudsters.
“We are working tirelessly to find a way to get the affected social media companies to take action.”
The charity thanked everyone for their support and understanding on this.
“It’s a sad world where someone would want to target a life-saving charity.”
“We will never ask for payment details or personal data through these social media platforms.”
Wales Air Ambulance covers the whole of Wales and needs to raise £8m each year to operate the service.
“Each year we take part in over 3,500 missions by air and road, covering the rural countryside and our bustling towns and villages. This includes the length of our Welsh coastline and across our vast mountain ranges.
“We rely entirely on public support to help keep the helicopters airborne.
“The charity does not receive direct government funding and we are not eligible for National Lottery funding.
“Our helicopters are kept airborne through charitable donations, fundraising events and membership in our in-house rescue lottery.”
The matter was reported to the police.