The man who is investigating the alleged Joost van der Westhuizen sex tape is urging the makers of the film to come forward.

Tabloid magazine Heat published pictures from the video, featuring a man it claims is the former rugby player involved in sexual acts with a woman, other than his wife, Amor Vittone. The man is also seen sniffing a white substance.

Van der Westhuizen hired private investigator Mike Bolhuis to look into the matter.

Bolhuis said they are calling on those involved in making the tape to make themselves known.

"This investigation is done on a neutral basis without anybody being influenced in any manner, to come forward and we would protect their identity. By Friday night, we would be finished more or less with all the offers given to people to assist us in this investigation," said Bolhuis.

Meanwhile, Heat magazine is sticking to its story and has requested Van der Westhuizen to make a clip of his voice available to be forensically analysed.

It said it is complying with Van der Westhuizen not to broadcast the video on its website, until the investigation is complete.