The force, which polices the rail and underground networks in England, Wales and Scotland, has warned the month of December had the highest number of thefts and robbery reports in recent years.
Superintendent John Loveless said during the autumn and winter months offenders operated under the "cover of darkness" to target people. "The nights drawing in earlier, it gives people an opportunity... for offending," he added.
BTP says there are three main "gadget-grabbers tactics" to beware of:
Niall, a musician and actor who has lived in London for 12 years, reported his phone theft to police. But he said he had not immediately thought to call his bank or cancel his cards.
"They took everything," he said. "My online banking was showing zero... zero... zero."
Niall explained the thief had taken out a £7,000 loan in his name from HSBC, transferring all of the cash to his Monzo account, and had then taken it all. Transactions showed the thief had gone on a "spending spree" in an Apple store, he added.
"It's one of those moments where you just in one second feel a bucket of sweat come out of your head and you go red," he said.
"It was panic stations for two days. I was on the phone pretty non stop... and then pacing up and down the kitchen. Just trying to get to the bottom of it."
"I've no idea how they'd got into either of my accounts," he added. "It's face ID and password protected. They managed to take out a loan, which is a laugh because I've been trying to get a loan for years and I'm not eligible for one - somehow they managed to."
British Transport Police advises people to: