Apple cannot help you locate your phone. Once option was to activated Find My iPhone on your device before it was lost or stolen. In that case, you could use Find My iPhone on iCloud to track it down if it remained online.
I suggest you follow Apple's advice on what to do now. Especially if you did not have it locked with a PIN code.
If you had enabled "Find my iPhone" you might have had a tiny chance of tracking it, but your question makes it clear that you did not set it up. You don't call Apple, they only make the thimgs.
Tell your carier.
Tell the Police.
Tell your insurance company.
Change any passwords that are compromised.
Buy a new phone.
"How can I get it back?" - catch the thief before he sells it.