How can i help my friend find his phone with my phone

The only way that you can help him is if he is sharing his location on Find My iPhone > People, or using a location services app like Life360. If none of those are true, he can only find his phone using other Apple devices connected to his Apple ID. If he doesn't have any other Apple Devices, he can visit www.iCloud.com/find and login with his Apple ID, and continue there.

Find My - Official Apple Support

If he lost his phone in a place like his home, you can help him by calling his phone number, and listening for ringing.

If he lost it out in some public place, and he wasn't already sharing his location with you, there isn't much that you can do. However, if he had Find My enabled on the phone, he could mark the phone as Lost, and try to track it … using a Web browser, if need be.

Find your lost iPhone or iPad - Apple Support

If your iPhone or iPad was stolen - Apple Support

Do's and Don'ts for lost iPhones - Switched Off - Offline - Beware of Phishing – Apple Community