how to find my iphone 6plus if its wifi turned off?

You might not see your device on iCloud.com or the Find My iPhone app for one of these reasons:

• iCloud isn't set up on your device. Choose Settings > iCloud and sign in with your Apple ID.
• Find My iPhone is turned off on your device. Choose Settings > Find My iPhone > turn on Find My iPhone and then tap Allow.
• You’re signed in to iCloud with a different Apple ID on your iOS device. Sign in to Find My iPhone with your other accounts until you see your device.
• Your device isn't connected to a network. If you have access to your device, and it appears to have an active Internet connection, turn on and then turn off Airplane mode. If you continue to have issues, turn the device off and back on. Find My Mac can only find your Mac if it's connected to the Internet from a known Wi-Fi network. If your Mac is connected to the Internet by an Ethernet cable, Find My Mac can't find your computer.
• The date on your device (iPhone, iPad, or iPod Touch) isn't correct. Choose Settings > General > Date & Time to check and set the date.

Above information from here > Get help using Find My iPhone - Apple Support