Can I report stolen iPhone if I just logged out of iCloud on that phone?
If you just logged out of iCloud on your iPhone, Find My iPhone was most likely also turned off, so it won't be of any help to you. However, if you didn't logout of iCloud, and the device is just offline, anything you set in Find My iPhone will be applied the next time your phone connects to a network.
Meanwhile, Apple suggests to:

Report your lost or stolen device to local law enforcement. Law enforcement might request the serial number of your device. Find your device serial number.
Report your lost or stolen device to your wireless carrier. Your carrier can disable the account, preventing phone calls, texts, and data use.

Good luck.