The pair, described as being in their late 20s to early 30s, were in a dark-coloured saloon car and stopped beside the 75-year-old as he left his house in Blackburn, West Lothian.
The women tried to sell the pensioner various items of jewellery by placing rings in his hand and putting a chain around his neck.
But the man refused to buy any and the women got back into their car and sped off at around 12.45pm on Saturday.
The victim then noticed that the women had removed his own gold chain with a large St Christopher medallion from around his neck and contacted police.
Both women are described as being of Asian appearance, approximately 5ft 7ins tall with medium builds and long dark shoulder-length hair.
They were wearing loose-fitted scarves over their heads.
The driver of the car is also described as being of Asian appearance, in his 40s with a medium build, dark hair and a moustache. He was wearing a light blue shirt.
There may also have been a child in the front passenger seat.
A police spokesman said: "These women have distracted the elderly victim by trying to persuade him to buy jewellery before making off with the chain from around his neck.
"Anyone who remembers seeing the suspects or the vehicle they were driving is asked to contact police immediately.
"Similarly, anyone with any other information that can assist with our enquiries is also asked to come forward."
Anyone with any information can contact Lothian and Borders Police on 0131 311 3131, or the charity Crimestoppers in confidence and complete anonymity on 0800 555 111.