It's not working for me to sign into find my iphone

If it does not show up possibilities are that the Find My iPhone is not enabled on the device

Set up Find My iPhone on all of your devices - Apple Support

It would be better if you can please post a screenshot, in order to understand the phenomenon better.

You may get better and prompt responses if you may kindly provide the iPhone Model that you have and the iOS version if it is known to you.