The so-called 'Glow Run' is scheduled for Derry's Ebrington Square on 21 November, with a number of local charities involved.
But the charities are now withdrawing from the event, having failed to make contact with the organisers, Endurance Junkie.
Another run, organised by the same company, was planned for the Stormont Estate on Saturday, but the tourist information site Visit Belfast says the event has been cancelled.
June Harpur signed up to the Derry run five months ago to raise money for a meningitis charity.
Her team of 12 family and friends spent around Â£500 on registration fees and branded t-shirts. They began training six weeks ago.
The Derry woman has been trying to get in touch with Endurance Junkie since September to confirm the details of the event, but has heard nothing.
Although the charity's logo was visible on posters advertising the event, its representatives informed June that Endurance Junkie is an independent organisation and not linked to theirs in any way.
"They explained that none of the registration fee was actually going to Meningitis Now, that was only to fund the run."
June made several attempts to contact Endurance Junkie but was unsuccessful.
"We tried emailing them, tried phoning them," she said.
"The emails are going unanswered, the phone lines and mobiles are all out of service. There was a Facebook and Twitter account but they've been taken down.
"My concern is that this run won't go ahead, we won't get a refund and Meningitis Now won't get their money back. I'm just at a loss as to how someone could organise something, advertise that it's for charity and then just disappear."
The BBC tried on several occasions to get in touch with Endurance Junkie. So far, they have not returned the calls and their website is now offline.
A Londonderry mother, whose young daughter almost died from meningitis, has raised concerns about a charity run due to take place in the city in November.