The price of the shares has fallen 93% since peaking at 705p six months ago. They fell from 195p at the beginning of this week to 52p after the group announced on Tuesday it would post a £5m loss for the half year to 30 September and would cut 400 jobs.
Chief executive Robin Southwell left on Monday by "mutual agreement" and is expected to receive a £360,000 pay-off.
Atkins staff own 23% of the company, some of them through employee benefit trusts. They have watched helplessly as the value of their holding has fallen from £152m to £12m over six months.
A source at Atkins Faithful & Gould, the firm's QS business, said: "The mood is muted. We're a bit shocked, to be honest. Everyone's a bit concerned because it is a parent company – but the directors are putting a positive spin on things."
Atkins said its full-year pre-tax profit would be about £15m, or £28m less than previously forecast.
About 200 of the 400 jobs losses will be in the UK, with 50 at the group's headquarters in Epsom, Surrey. The company employs 15,200 staff throughout the world.
Chairman Mike Jeffries, who is acting chief executive after Southwell's departure, conceded that the financial losses would hit staff morale. He said his priority was to stabilise the situation at the group.
"It's all happened extremely fast," he said. "My first concern is for our staff and investors who have been hit by this."
The value of Jeffries' own stake has fallen from £3.3m to £260,000. City investors own 60% of the group, the Atkins family 7%.
Jeffries said the company's mistake had been to do too much, too soon. He said Southwell had not been made a scapegoat, adding: "Everyone has to take their share of the blame, including me."
Southwell, who joined from weapons maker BAE last April, left Atkins on Monday – the same day that he appeared in adverts taken out by unions in national newspapers to accuse the PFI of "wrecking" public services. The campaign was sponsored by the GMB and Unison in the run-up to the PFI debate at the Labour conference this week.
Jeffries conceded that Atkins needed a chief executive who had an in-depth understanding of major technical projects as well as commercial ability.
Jeffries said the long-term outlook for the group was buoyant and described Atkins' problems as "self-inflicted". He added: "The good news is that we can fix it ourselves. It is a systems problem, not a problem with the business."
Atkins said its performance had been hit by problems with its billing, credit control and pay-roll systems. These had taken longer than expected to introduce and proved more expensive than anticipated.