It's probably already been mentioned but Dateline covered the story while it was still a missing persons case:
Family desperately searching for missing West Virginia teen Riley Crossman
So, if I have it right:
May 7, 3:30 pm - Riley woke her mother, Chantel, for work.
May 7, 7:00 pm - Riley's grandmother left Riley's home.
May 7, 10:00 pm - Chantel arrived home from work. Saw Riley's bedroom light on but didn't see her.
May 7, 10:30 pm - Riley finished video call with her boyfriend.
May 7, Midnight - Riley finished texting with a friend.
May 8, 5:40 am - Riley tried to video call her boyfriend but he was asleep.
May 8, 7:15 am - Chantel woke up and saw that Riley was gone but thought she'd already left for school which was across the street. (EDIT: Story said "across the street" but it appears she lived on Greenway which is about a quarter-mile away.)
May 8, 7:45 am - Riley's school started classes.
May 8, 3:30 pm - Chantel messaged Riley asking where she was because her grandmother had said she hadn't come home from school. Message didn't deliver. She then called and it went to voicemail. Second text went undelivered.
May 8, 3:40 pm (approximate) - Chantel asked her mother to go to school and look for Riley. Riley wasn't there.
May 8, 5:00 pm - Chantel left work and drove to school to look for Riley. Riley's boyfriend was in parking lot. He'd just returned from a school field trip. He hadn't talked to her all day. School then called Chantel and reported Riley had been absent that day. Chantel they called 911 and Riley's father, Lance Crossman, whole lived 25 minutes away.