Detectives have linked two offences within half an hour of each other in which a group of six males threatened teenagers at knifepoint for their mobile phones.
Officers have connected an attempted robbery and a robbery which happened between 8.25pm and 8.55pm on Tuesday, September 5, in the Carr Green Recreation Ground area of Rastrick.
On both occasions a group of up to six male culprits have approached the victims, police said.
The victims were able to provide descriptions of three of the suspects with an e-fit produced of one of the men.
The first culprit is described as white, aged in his early 20s, around 6ft 2ins tall, with a ginger perm which was around two inches in length. He was wearing a grey hoodie.
The second offender is described as around 5ft tall and was wearing a black hooded top, with a balaclava or scarf over his face.
The third suspect – pictured in the e-fit image – is described as Asian, around 19-years-old, approximately 5ft 10ins tall, of stocky build with a round face and large nose with dark, brushed down hair. He was wearing a grey hoodie with the hood pulled up.
Anyone who witnessed either of the offences or who saw a group matching the descriptions are asked to call Calderdale CID via 101 or independent charity Crimestoppers on 0800 555 111.