A relative of Ivan Milat has been refused bail after being charged with murdering a teenager in the Belanglo State Forest in southern New South Wales.

The ABC has been told the victim was celebrating his 17th birthday when he was killed.

Police found the body off a dirt track leading into the forest about 8:30pm yesterday.

It is the same forest where serial killer Milat dumped the bodies of seven backpackers he murdered in the 1990s.

Milat is serving a life sentence for the crimes.

Police say the teenager's relationship to Milat is irrelevant. This afternoon he was charged with murder.

Later in court the teenager did not apply for bail but the magistrate said it would have been refused given the nature of the crime.

Detectives are seeking forensic swabs off his hands, fingernail clippings and photographs of scratches on his body.

Another teenager has also faced court charged with being an accessory.

The court has heard he tipped police off about the death.

He has been refused bail and will face court again on Wednesday.

About 5:00pm (AEDT) a third teenager was also charged in connection with the death.

The acting commander of the homicide squad, Pamela Young, says the victim had suffered a violent death.

"He has been murdered and his body has been somewhat shallowly buried but also intentionally covered in debris down at the Belanglo State Forest," she said.

Police are still looking for the murder weapon.

They will not say how the victim was killed but say he was not shot.