Lost cat..?

This morning around 7 am, I woke up and noticed my cat wasn't by my side. This was completely fine, as she is free to wander and I assumed she would be somewhere else in the house. Turns out, shes nowhere to be found. My mom and dad were awake at this time and they were in the basement and didn't see her either. My dad left for work shortly after. I have turned my house upside down, and have not been able to find her. I've left food out and it hasn't been touched. My parents are assuming she's outside but how can this be possible when all of our doors were locked and closed? No one had even left the house at that point. I don't know what to do, I know cats get lost in the house but its been over 12 hours. Any advice would help, thank you.