find a stolen iphone with IMEI

You cannot track it with just the IMEI. You can report it stolen to your carrier, who can blacklist it so no one can use it, at least not in the country where it was reported stolen. But there is no world-wide blacklist, so most likely it will be shipped to another country. In some countries the police can track the approximate location of a stolen phone if it is powered on through the cellular network providers, but this requires a warrant (at least in the US) and you would have to interest the police in going to the trouble of doing it.

And yes, IMEI sites are scams almost universally.

You cannot track a phone with the IMEI number. See here for what to do: https://support.apple.com/en-us/HT201472