The search continued until light faded on Sunday night, and resumed again at first light yesterday.
Garda and the civil defence were involved in river and riverbank searches, and also used drones to scan a distance of the river from above.
Garda sergeant Ralph Holmes said the search was continuing along the river and the section of the Grand Canal beside it.
Locals and family members looked on helplessly from the Lock as the search was carried out.
Mr Reid’s partner, whose family said is seven months pregnant, also waited patiently and quietly for word.
The search involved a large number of rescue personnel from the gardai and civil defence, and locals brought trays of sandwiches and cases of bottled water to the scene to keep the crews fed throughout their difficult task.