An undated handout picture obtained from Police Scotland on January 17, 2014 shows missing three-year-old boy Mikaeel Kular.
Hundreds of volunteers searched around Edinburgh on Friday for a three-year-old boy who vanished from his bed.
Mikaeel Kular, who is of South Asian origin, was last seen on Wednesday evening when his mother Rosdeep put him to bed at their home to the north of the Scottish capital.
Police launched a major ground, air and sea search but failed to find any trace of the missing toddler, while more than 200 volunteers helped comb through woodland and the nearby coastline.
Officers said they were investigating reported sightings of a young boy spotted walking alone down a street close to Mikaeel's home on Thursday morning.
Assistant Chief Constable Malcolm Graham of Police Scotland said detectives were investigating the possibility that the little boy was kidnapped.
"It's of grave concern that such a young child has been missing for such a long time," Graham told reporters.
"It's entirely possible that Mikaeel has left the house of his own accord and all of our actions are attempting to cover that possibility. It is, however, entirely possible that Mikaeel has become subject to a criminal act."
"Specialist resources" from across Scotland have been deployed for the search, he added.