Q: My sister just lost her phone and is under my plan. How can I locate her phone?

If it's an iPhone and Find My iPhone set up for it, use that.

If it's an iPhone but doesn't, physically search for it, post notices around where it was lost, and report it to the police.

If it's a different phone, it depends on what type of phone it is.

(143278)

You would need to log into iCloud.com with her Apple ID and password and see if the device can be located. It would have to have had Find My iPhone activated, the device powered on, and have an active connection to the internet.

P.S. Not a good ideal to post a phone number to an international public forum. I've asked the hosts to edit it.

Also follow instructions here

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support