Trailing worker ants is a good way to find the nest. Ants are rarely active before 10am and cold, wet weather will also reduce the amount of worker ants foraging. Ants excavate to enlarge the nest and nest entrances usually have little ‘volcanoes’ of dry soil around them. Look for these both inside and out as they are good indicators of an active nest.
Where there are no piles of sand marking the entrance, there will be small holes. Try blowing gently into suspected entrances or tapping next to them – workers will usually emerge to defend the nest.
Having found one nest, do not stop looking. Ants invading a building are normally nesting within six meters of the building. Continue to inspect until you have found all the potential problem nests.