Client work has basically ground to a halt, said Marty Susz, account supervisor on Intel Corp.
"Intel has been incredibly understanding," he said.
Mr. Susz said he witnessed the attack on the Twin Towers from his office window along with 30 other people at the agency.
Messner's offices, at 350 Hudson St., were evacuated shortly after the second explosion, and about 400 employees began walking uptown and away from lower Manhattan.
About 50 to 75 Euro/RSCG employees, also housed at 350 Hudson St., evacuated with them.
"We fruitlessly tried to get hotel rooms," Mr. Susz said.
He and a couple of colleagues made it home to Westchester County by car in about two hours. Manhattanites offered colleagues from the outer boroughs a place to stay.
The Messner office is expected to fully re-open on Monday.