Al Jazeera's Rosiland Jordan in Washington said: "This has turned from an afternoon drama on the cable television news channels into now perhaps a criminal investigation.
"Authorities say they searched the family's home when they first got the report that the child was missing, but when you're considering that we're only talking about a span of three hours or so, you have to wonder how thorough was this search, have they really looked at all the possibilities about the whereabouts of this boy?"
The balloon was capable of flying to an altitude of about 3,000 metres, a height where oxygen is in very short supply.
Helicopters followed the silver balloon, which was reportedly made by the boy's father.
The balloon's basket was enclosed, making it difficult to asceratin whether anyone was trapped inside.