At around 12.15am on Friday 16 August 2013, the man was walking home from the Three Tuns pub in Market Place when he was approached by a group of people on Hambleton Place.
One of the group punched him the face and stole his black iPhone 4.
Officers have arrested two men aged 19 and 20 in connection with the incident. They remain in police custody for questioning.
Despite the arrests, officers are urging anyone who witnessed the incident to contact them with information.
Anyone who can help the investigation is urged to contact North Yorkshire Police on 101 – select option 2 – and ask for Detective Constable Lee Allenby or Northallerton CID.
Alternatively, information can be emailed to email@example.com
If you wish to remain anonymous, Crimestoppers can be contacted on 0800 555 111.
Please quote reference number 12130140129 when passing information about this incident.