A necklace has emerged as a potential vital clue that could help find an Australian tourist who vanished in California three weeks ago.

Sally Grace Contarino, 26, was due to fly home to Melbourne on June 21, but did not make her flight and has not been heard from since.

She was last seen on CCTV on June 20 leaving a supermarket in Skye Canyon, northwest Las Vegas, as she was headed towards nearby Mount Charleston.

Local social media page Real Vegas Locals have shared updates on behalf of Ms Contarino’s sisters, Lauren and Amy. Both women are currently in Las Vegas helping the search for their sister. 

However, they’ve been unable to find a necklace their sister was gifted by a relative, despite her luggage being left at her accommodation.

The 26-year-old was known to always wear a distinctive necklace – a citrine pendant on a silver chain from luxury jeweller John Hardy.

‘If Sally was wearing the necklace, someone may have seen it, found it, or come across it without realising its significance,’ Real Vegas Locals wrote.

Sally Grace Contarino (above) was last seen in Las Vegas on June 20, the day before she was due to fly home to Melbourne

Ms Contarino was known to wear a distinctive necklace (above), a citrine pendant on a silver chain from luxury jeweller John Hardy

‘It may also be worth keeping an eye on online marketplaces such as eBay, Facebook Marketplace, Poshmark and similar sites.

‘Every detail, no matter how small, could be important.’

A Las Vegas Metropolitan Police Department spokesperson told 9News officers ‘continue to exhaust every lead but encourage anyone with information about her whereabouts to contact us’.

Interest in the missing necklace comes after one of Ms Contarino’s final messages before disappearing was revealed.

A Las Vegas Metropolitan Police report, obtained by local broadcaster 8 News Now, claimed Ms Contarino had messaged a male friend on June 19 on Facebook shortly before her disappearance.

A fan of California’s scenic landscapes and a keen hiker, she had shared plans to hike at Lone Mountain, which offers views of Mount Charleston.

Ms Contarino was travelling alone. It is unknown if she’d planned to hike alongside someone else.

Lauren, Ms Contarino’s sister, told Real Vegas Locals the missing Australian had hiked Mount Charleston the next day instead, before she vanished.

On June 19, Sally had dinner at Timbers Bar and Grill, near Summerlin

Mount Charleston features several hiking trails and fluctuating temperatures

Sally had checked out of Bungalows Hostel but left her luggage in storage

‘She was definitely on the mountain. It’s confirmed she did make it for her walk up there,’ Lauren said.

‘We don’t know if someone picked her up afterwards, it’s possible.’

Hundreds of dedicated Las Vegas locals have volunteered to help find Ms Contarino, along with more researchers online who’ve worked to help piece together a timeline of her disappearance.

‘Members are reviewing maps, bus routes, hiking trails, CCTV locations, weather conditions and publicly available information while working to separate confirmed facts from speculation,’ Real Vegas Locals said.

‘Vegas locals have also been sharing firsthand knowledge of the Skye Canyon and Mount Charleston areas, helping explain the terrain, neighbourhoods and hiking conditions.

‘Locals have been reviewing old dashcam footage, hiking areas Sally may have visited, following possible footprints, flying drones and sharing photos and information they believe could assist investigators.’

Concerns for Sally’s welfare were raised after she did not return for her luggage, which she’d stored at Bungalows Hostel after checking out from her dormitory on the morning of June 20.

Ms Contarino was reported missing when she failed to board her flight from Los Angeles to Melbourne on June 21.

She had arrived in the US on June 13.

Anyone with information about her disappearance is urged to contact Las Vegas Metropolitan Police Department.