they find the shoe of the missing girl and don't tell the police?
Why wouldn't they?
A police Squad would have immediately searched the whole canal system.
Otherwise well done film - which lacks a bit of tense when you know the original movie.
SPOILERS:
The authorities in Derry know something horrible and evil is killing people here and there, and they're at a loss to figure out how the killer keeps getting away with it, leaving no physical evidence of a crime except the mutilated remains (when IT leaves them, that is). The idea is so horrible that they pretend it doesn't happen, which could be being engineered by IT itself, manipulating the minds of adults to find scapegoats for the murders and diverting attention away from IT itself. With that kind of situation, the children of Derry sympathise when their peers, friends and relatives go missing, but they keep it to themselves. It's the Losers, whose leader, Bill, suffered the loss of his brother at IT's hands, who band together to investigate the cause and to confront IT when the adults won't.
IT Chapter 2 / Book spoiler:
As an example of IT diverting attention away from itself when it kills, when IT returns after 27 years, it brutally kills a local gay man called Adrian Mellon, and two homophobic men are arrested for the crime, but no evidence is found that they did it, so the authorities are at a loss.
But when I watch a movie I jugde it on its own not by the book it is based on.
And they showed the mother of the missing girl actively searching for her kid. Our heroes saw her - found that shoe later and told nobody! That felt so wrong. If they gave the shoe to somebody and this somebody wouldn't have acted on it because of Its influence - that would have been enough - to see them try.
But as presented in the film. It didn't made sense to me and bothered me a lot.
You make a fair point about the book, and that the movie should stand by itself, but here's hoping that Chapter 2 will explain things in much greater detail. That's bound to happen since the Losers Club will be adults in that. I personally look forward to it.