Around 100 police officers have been assigned to physically searching the countryside around the Rhineland town of Grefrath while the detective team has been expanded to 80.
Detectives were visiting house-to-house on Saturday, speaking to residents and asking them whether they had either spotted the boy Mirco, or anything out of the usual.
Information is being sought about a car seen near the spot where Mirco's bicycle was found on Friday, while posters are being put up asking for witnesses – on the other side of the nearby Dutch border as well as on the German side.
Mirco's trousers were found by a woman who initially took them home before realising they were connected with the missing boy and handing them over to police. They are being examined for DNA traces in an attempt to find any connection to a perpetrator.
The boy was last seen at a bus stop last Friday near a skater park in Grefrath, where he was supposed to ride his bike home, but he never arrived. His parents, who have three other children, are being counselled by psychologists.