Hundreds of Calgarians and people across Alberta released green balloons into the skies above the city Tuesday night in honour of Nathan O'Brien.

A Facebook group organizing the balloon release was started Monday after police announced that evidence has led them to believe five-year-old Nathan O'Brien and his grandparents, Kathy and Alvin Liknes — who have been missing for more than two weeks — have been murdered.

"It's important the O'Brien/Liknes family is aware of the army of support they have standing behind them," said the group's Facebook page.

By releasing the balloons, the group hoped to "fill the sky with love and prayers throughout the entire city, and show our support."

The colour green was chosen because a green ribbon is a recognized symbol to remember missing children.

Green ribbon campaign

Lorri Swinson, a neighbour of Alvin and Kathy Liknes, had started a green ribbon campaign earlier in the investigation.

"I think deep down I felt that there was likely going to be a tragic outcome but the reason we started this campaign was to show support because Mr. and Mrs. Liknes are members of our community," she said.

She said many people were in shock after police announced the missing family case is now a homicide investigation.

Douglas Garland, 54, has been charged with two counts of first-degree murder for the deaths of the Likneses and one count of second-degree murder for Nathan's death.

Albertans took to Twitter to grieve with the family. On mobile? Click here to see some of their posts.