The final steps of a Sydney teenager believed to have been bludgeoned to death, Mahmoud Hrouk, are being traced by NSW Police and the boy's family.

Formal identification of a body found at a house in Fairfield West on Sunday has not yet been confirmed, but police believe it is that of the 16-year-old, who was reported missing a day earlier by his parents.

His parents made the grim discovery, when they looked through the window of the house finding a bloodied and lifeless figure inside.

Police said yesterday the body found in the house was that of someone who had been brutally bashed and sustained serious head injuries.

A blue-and-silver mountain bike Hrouk had been seen riding on Saturday night was found about 200 metres away from the house where the body was found, police said.

Officers said yesterday that the teenager had never been in trouble with the law and was not believed to have been involved with drugs.

Police returned to the house on Monday, taking away bags of evidence and dusting a red sedan for fingerprints.

Mahmoud, a former student at Granville Boys High School, last spoke to his parents at 9:30pm AEST on Saturday night and was seen at McDonald's in Villawood three hours earlier.

Police are still working to determine whether the deceased person was killed at the vacant house.

Anyone with information should call Crimestoppers on 1800 333 000.

ABC/AAP