what does the newscast reveal to montag? why does the tv present this

It basically reveals that Montag is wanted for crimes against the state. They want anybody who has seen Montag to alert authorities.

Before Guy leaves, Faber shows him a small television screen – the size of a postcard – in his bedroom. They turn to the news and watch the chase scene in progress. Since Montag flamed the town’s Mechanical Hound, a new one has been brought from the neighboring district.