Sinn Féin Councillor Brian McGuigan said people from the parishes of Ballinascreen and Desertmartin were travelling over during the day and evening to carry out searches along the banks of the River Foyle.
He said a special prayer service has taken place in Keenagh Chapel and the searches would be ongoing till Helena was located.
The mother-of-four young children was last seen on Sunday, November 24.
Councillor McGuigan said he travelled over to Derry City on Monday and there were around 70 people taking part in the searches.
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“We met up at the Sainsbury car park and the professional searchers split up the party into three different groups,” he explained.
“It’s a big community effort to try and find her and show support for the family who are desperate.”
PSNI Sergeant Adrian Brogan said the 42-year-old was last seen at around 11am in the area of the lay-by on the city end of the Foyle Bridge.
“It’s believed Helena had got out of her vehicle - a black Mitsubishi Outlander - at the lay-by and, at this time, she was wearing a long brown, possibly black dress,” he said.
“In a bid to trace Helena’s last movements, officers will be at the lay-by on the Foyle Bridge this morning where she was last seen and where her vehicle was located.
“Our officers will be distributing leaflets in a bid to jog people’s memories.
“The Mitsubishi will also be at the lay-by.
“Helena is described as being 5’ 4’’ tall, with short dark hair and of a slim build.
“I want anyone who was in the area last Sunday, either driving or walking, around 11am to think back about who you remember seeing.”
Councillor McGuigan, who has visited the family, added that they are “just hoping against hope” that she will turn up.
“They can take some comfort from the fact that they have the full support of the local community at this difficult time,” he added.