If I turn my iPhone off, can my friends still track my location?

It depends what you mean by off. If you shut it down by holding the sleep/wake button down, then use slide the "slide to power off" button, I'm pretty sure you won't be trackable. You can test it with Find My Phone. . . . I just tried it. You cannot be tracked if it is powered down. That would include a dead battery.

Hello Tarrytie,

There is a very easy way of hiding your location from your friends:

Open Find My Friends and tap on yourself. Then turn off Share My Location.