Ransom!

Ransom is a 1956 crime drama examining the reactions of parents, police, and the public to a kidnapping. Written by Richard Maibaum and Cyril Hume, the film was based on a popular episode of The United States Steel Hour titled Fearful Decision, which aired in 1954, starred Ralph Bellamy.

Young Andy Stannard Bobby Clark is the son of Dave Stannard Glenn Ford, a wealthy executive, and his wife Edith Donna Reed. One day, Edith and Dave feel that each has miscommunicated with the other about the whereabouts of their son. The principal Mrs. Partridge Mabel Albertson of Andys school telephones and informs Edith that Andy was picked up by a nurse and taken to Dr. Gormans Alexander Scourby office for treatment of a viral infection. However, when Dave phones Dr. Gorman, he finds out that Andy has not been at his office at all that day. Realizing that their son has been kidnapped, the Stannards call the police.The chief of police Jim Backett Robert Keith organizes a search for young Andy. He directs the installation of traces on the four telephone lines into the house, and he has a dummy line created for all outgoing calls, in order to keep the main number free. Together, they are waiting for the kidnappers to call with a ransom demand when newspaper reporter Charlie Telfer Leslie Nielsen slips into the house to observe the goings on. Backett attempts to throw him out, but Telfer, who is a friend of Backetts, manages to stick around for the kidnappers phone call. ........

Source: Wikipedia