I have been trying to find background information for free on the internet of a guy I've just met who has promised me the world. Can someone tell me a website to use to find out any information I can for free

Try googling his name.

Before you can locate this person you need some personal information such as date of birth, place of birth, maybe family members name, where he currently resides, phone number or better yet SSAN.

Google free people locator and some will allow you a free membership for a few days but it does require some information about the person especially if they have a common name you need something to ensure it's indeed them. But if the person is a con doesn't matter what you use will not be able to locate so if you can get a phone number or address so you can do a reverse search. Hope that helps?