The victim, a 19-year-old man, was walking alone on Old Park Road, Roundhay, on November 6.
He was approached from behind by three offenders, who threatened him with a knife and demanded he hand over property at about 7.20pm.
The victim gave them his mobile phone and wallet.
They fled into Roundhay Park.
Police today have appealed for any witnesses to the robbery to come forward.
Anyone with information is asked to contact police on 101, quoting crime reference number 13170518543.