Diana Linu, who is from Romania, was reported missing on February 14.
The teenager has not been heard from since she spoke to her father in Romania late on the evening of February 13.
Hounslow Police posted an appeal on Twitter at 7.50pm on February 14.
It reads: "Please can you help us find Diana LINU who has been reported #missing from #Hounslow.
"Any info call 101, quote ref: 17MIS006732.
Anyone with information as to the whereabouts of the teenager should call police on 101, using 17MIS006732 as a reference.
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