I really enjoyed reading The Insomniacs by Marit Weisenberg. I feel like mysteries and thrillers are hard to find in the YA space without adding in fantasy elements. I started reading this on Halloween and it was the perfect amount of spooky-ness for the day. I was fully invested in the characters and while I had some idea of how the story would end, I did not predict the journey. The love-story was really well done too, with just enough to satisfy your need for a teen love story, without taking over the mystery and the atmosphere. I'd definitely read more of Weisenberg's books and I hope they keep writing.
If you enjoy Karen McManus, or adult thrillers, you'll enjoy this fast paced read.