Hey there! I'm so sorry for the delay in reply to your question. Is your phone missing, or were you just curious for general reasons?
The order of operations is up to interpretation, because once you suspend your line, your device won't have data access to track. On the other hand, leaving the line enabled means that if you didn't have a lock screen on your phone, whoever's found it could potentially rack up charges for things like international calls using your device! It's ultimately up to you whether you'd like to try to use Find My iPhone or go ahead and report the issue to us immediately, but I wanted to call out that most tracking services won't work unless the device has a data connection, but leaving it on could be dangerous.
Last but not least, if you do have insurance, make sure to initiate the claims process before you start using a temporary device! The insurance covers whatever phone was most recently used on the line; so if you want it to cover your iPhone, please contact the insurance agency before you switch to a different phone!
Apple's page on using Find My iPhone: Find My iPhone, iPad, Mac, and Apple Watch - Official Apple Support
Our page which walks through suspending your line, reporting the device, and contacting insurance if that's an option: Replace a lost or stolen device
Please let me know if you have any other questions -- and again, I hope your phone isn't missing!
I'm also going to send a PM your way about your username. Please take a look in your inbox in a few! Thanks.