Detectives appealed for public help today to trace a six-month-old boy amid fears that the child may be dead.
West Midlands Police said four people had been arrested in connection with the disappearance of Troy Simpson, who was reported missing from his home in Smethwick yesterday.
Addressing a press conference in Birmingham, Supt Andy Bebbington said he fervently hoped that Troy was still alive.
The officer told reporters that the mixed race child disappeared after being put to bed on Monday night at his home in The Uplands, Smethwick.
Troy - who is not thought to have been taken by an intruder - was reported missing after his grandmother noticed that he was not in his bed yesterday morning.
Mr Bebbington said: "It's suggested that he was put to bed at approximately 9.15pm on Monday and that by 6am the following morning he was not in his bed.
"I fervently hope that Troy is alive but I have to accept the possibility that he may be dead.
"There are a number of possibilities in this case and I am here today to appeal to members of the public in that area to search their houses, to search outside, in gardens and on wasteland near to them in order to try and find Troy.
"I have at present four people in custody in relation to this matter but despite that fact I do not know whether Troy is alive or dead."
The detective said the house was "in a state where an intruder would have been very unlikely to be able to enter" and to remove the child.
The superintendent continued: "There is a possibility that Troy is being held by somebody and that he's alive and well.
"In that event, I would appeal to anybody who has any knowledge of Troy's whereabouts to please contact us immediately.
"There are circumstances around this matter that lead me to believe that his death is a possibility.
"As you can imagine, we are taking this matter extremely seriously and there are a large number of officers involved in the inquiry."
Troy lived with his mother and grandmother although his mother is not thought to have stayed at the house on the night the baby disappeared.
Police have refused to say whether Troy's mother is among the two women and two men who have been arrested, although some of the individuals in custody are said to be "related" to the youngster's family.
Anyone who can assist the inquiry is urged to contact detectives at Smethwick police station on 0121 626 9148.