Published Wednesday, 26 December 2012
Police investigating the theft are appealing for witnesses. (© UTV)
The victims were approached by two boys, aged around 17, on Belfast's Bank Street on Christmas Eve at around 2.30pm.
One of the youths had his mobile phone stolen. Although the boys were not injured, they were left shaken.
The robber, who was carrying the knife, was described as being approx 5ft 10in tall and of slim build. He was wearing a light coloured hooded top concealing his face.
His assailant was described as being 6ft tall, of slim build and was wearing a hooded top with a grey scarf covering his face.
Police investigating the incident would like any witnesses, or anyone with information, to come forward.