Euan, from Croydon, was last seen near Waterloo station just before 8.10pm yesterday (January 13).
Officers say the 15-year-old is believed to be using trains from the station.
If you see him or have any information on his whereabouts call 999 and quote reference CAD 5169/13Jan.
A spokesperson for the Metropolitan Police said: “Police are concerned for the welfare of Euan, 15, who is missing from Croydon.
“He was last seen near Waterloo Station at 20.06hrs and is believed to be using the trains.
“If you have any information or have seen him please call 999 quoting CAD 5169/13Jan.”
