Family and friends of an Alberta couple who have been missing for nearly three weeks plan to hold a "vigil of hope" on Saturday.

Marie Ann McCann and Lyle Thomas McCann left their suburban Edmonton home for B.C. on July 3 and have not been seen by their family since. (RCMP)

The Edmonton-area vigil "is an opportunity for everyone to gather together to show support for the family," according to an online notice, as well as to support the search for Lyle McCann, 78, and Marie Ann McCann, 77.

The McCanns' son, Bret McCann, and his daughter, Nicole, will attend.

"Hopefully, this will get the word out about our parents [being] missing and hopefully it will help us find our parents safe," Bret McCann said.

His parents were last seen at a gas station July 3 while on a road trip to the Vancouver area.

Two days later, the St. Albert couple's motorhome was found burned to a shell at a campground 200 kilometres west of Edmonton. But the police investigation didn't begin until July 10, when their daughter reported them missing after they didn't meet her as planned at the airport in Abbotsford, B.C.

Saturday's candlelight vigil starts at 7 p.m. MT in the front plaza of St. Albert Place in St. Albert.

Lighting candles

Vigil organizers ask anyone who wishes to support the vigil but is unable to attend, to light their own candle or turn their porch light on.

In a Facebook group called Help Us Find Our Parents, friends and family are expressing their hope to see the McCanns again. Nearly 35,000 people have joined the group.

"I pray that God will see how many people are wanting the McCanns home, where they belong, and he will lead them home," one poster wrote.

The police investigation has recently focused on another campground west of Edmonton and on a house in nearby MacKay, where Travis Vader, whom police describe as a "person of interest" in the case, was arrested Monday.

RCMP officers spent much of Wednesday combing through the house and removing boxes of materials.

Vader remains in custody on charges unrelated to the McCann case. No charges have been laid against anyone in their disappearance.