A girl believed to be just 13 targeted a pensioner in an elaborate scam last Friday.
The youngster knocked at the 83-year-old's door in Walnut Tree Road, Hounslow, at about 6pm and asked for some paper to leave a note for a friend.
She distracted him by asking for a glass of water, allowing a male associate to make his way inside.
However, the pensioner became suspicious and ordered them both to leave before they could take anything.
The girl is white, very slim and had collar-length brown hair with a fringe. She was wearing a blue cardigan and jogging bottoms.
The man is white, aged 15-20 and had bushy brown hair.
Anyone with information should call Hounslow CID on 020 8247 6133.