Thieves grabbed mobile phones from train passengers before dashing across tracks to escape.
A man snatched an iPhone out of a woman's hand on a train as it pulled into Mill Hill Broadway, around 9.30pm on September 11.
The man, who boarded at Kentish Town, left the train, and ran across the tracks to escape.
Police officers believe the same man was joined by an accomplice four days later, when the pair snatched two iPhones from a man and a woman on a train travelling between Cricklewood and Hendon at around 9.45pm on September 15.
The men grabbed the phones as the train arrived at Hendon, and ran across the tracks to escape from the station.
Officers believe one of the men may have a tattoo with the name Kaya on his neck.
CCTV images have been released of men police want to talk to in relation to the thefts.
Anyone with information should contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference ESUB/B7 of 13/10/2014.
People can also contact Crimestoppers anonymously on 0800 555 111.
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