It happened between 8.10 and 8.20am on Wednesday, January 5 in Fartown.
The young girl was approached by a man as she walked by the entrance of a park.
The man grabbed her and took her to out-buildings near the old Fartown Rugby Club pitch off of Spaines Road.
He then seriously sexually assaulted her.
After the attack, the girl fled the area and went to get help.
T/Detective Superintendent Tony Nicholson of the Homicide and Major Enquiry Team, said: “This is clearly a very serious incident in which a teenage girl has been seriously sexually assaulted.
“She has been receiving care from professionals and specialist police officers.
“Such attacks are fortunately very rare in our communities and I can promise residents that all possible efforts are being made to investigate this attack and locate the person responsible.
“Officers from the Huddersfield NPT have also stepped up patrols in the local Fartown area to reassure nearby residents.
“We are appealing for witnesses and would like to speak with anyone who saw the suspect who is described as light skinned, of dual heritage, in his late 20s, around 5ft 7ins tall, broadly built and as having short cropped hair. He was described as wearing dark clothing.
“Anyone who saw a man fitting the suspect’s description either entering or leaving the old rugby club area or Spaines Road just before or after the attack is asked to contact us.
“Information can be given to HMET on 101 or online at www.westyorkshire.police.uk/101livechat All reports should reference crime number 13220005641.
“Reports can also be made anonymously to the independent Crimestoppers charity on 0800 555 111.”