The Nightworld by Jack Blaine

Scraping by in classes, hanging out with his best friend Charlie, and trying to get a date with Lara Hanover, the prettiest girl in school—that was Nick Robbins’ life.

Survival was the last thing on his mind.

Then, a strange cloud appeared over the city. A cloud that kept growing. The darkness on the horizon consumed the light around it. And Nick’s dad, a Department of Defense energy physicist, might have something to do with it. Soon, it became clear that the world Nick knew would never be the same.

Now, night is never-ending. The temperature is falling as heat leaves the world. Plants and animals are dying and people are turning into predators waiting for any small advantage. But Nick is determined not to disappear like the fading light. Desperate to glimpse a familiar face in the shadows, Nick races to find his friends—and the one clue that’s his glimmer of hope (info from Goodreads.com)

Going into the story I couldn't help but be reminded of some of the post-apocalyptic novels I have read recently, such as Ashfall by Mike Mullen and Dark Inside by Jeyn Roberts.
This book was not quite as long or intense as those reads, but I definitely got the same kind of vibe. A boy who's father hides him in a closet when he fears a group of people are coming for him, witnesses his fathers death. Before shooting him they ask for a device, which he refuses to help them find. In a panic he decides to go to his friends abandoned house to hide out until things cool down some. There has just been a recent event that has caused a dark cloud to hang over the city, several people have left and murders and stealing has run rampant. When he starts to run out of food he decides it's time to move on and find different shelter and food. He also gains a companion, a dog.
There is the mystery of the black cloud, the device and what his father was doing that caused the men to come after him. It seems that the device the men were looking for maybe something Nick can get his hands on and save the world.
There is a romance and Nick makes both friends and enemies as he tries to figure out what is going on.
It is a pretty interesting and sometimes intense read, not anything that would give you nightmares, it does have a cliffhanger ending though and I anticipate a lot of action and activity going on in book 2.