ACT Policing appealed for witnesses to the suspicious fire that destroyed the Mediterranean restaurant Avesta and damaged nearby businesses in the early morning of November 29, forcing the neighbouring Greater Union-owned cinemas to close temporarily.

Four pumpers, the breathing apparatus van and two commanders attended the scene, and crews were undertaking ventilation operations the next morning.

On Wednesday, a police spokesman said they were following a number of lines of inquiry but could not detail them.

"Forensic examination of items seized at the scene are being undertaken however it is suspected that an accelerant was used."

He said they were still searching for a man who was riding a bike at the time of the fire and repeated the call for that man and any other witnesses to come forward with information.

"The site has been handed back to control of the owners of the building," he said.

The restaurant had been vacant since Avesta occupied it for six months from Christmas last year to July.

The building owner Sotiria Liangis declined to comment.

A manager at the Capitol Cinemas, which also sustained smoke damage, said they had been working tirelessly to repair the building. The cinema re-opened Thursday morning.

A post on the cinema's Facebook page said "the repairs to our cinemas are more extensive than first estimated," as they had initially planned to re-open on December 2.

Multiple businesses along Franklin Street, including My Cafe and Down Town Milk Bar, reported a drop in trade during the week the cinema was closed.

My Cafe worker Tom Mendoza said he had noticed a quieter nighttime rush when customers would usually wander over for a coffee and cake after their movie.

Before being home to Avesta, the site previously housed Pheast and Charlie Black's Brasserie.

Police urge anyone with information to contact Crime Stoppers, anonymously if they wish, on 1800 333000.