how can i find my iphone when the apple id is an google account and i dont know the password

How did you log into this forum? An Apple ID is needed for that.

Note that it is possible to use a gmail email address for your Apple ID but that your password with Apple would usually not be the same as the password you use with gmail.

If you have another and have forgotten the ID or password, see the following:

If you forgot your Apple ID email address or phone number - Apple Support

or

If you forgot your Apple ID password - Apple Support

Your Apple ID is say example1@gmail.com if you don't remember as the iPhone is lost and it was signed in the device , without knowing the complete address nothing can be done ( password is also lost but it will loose its importance ) , assuming this is the only single device that was not synced with Mac .