If someone is using your personal information please use the Contact Us form or report the ad through the website.
In order to report an advert you will have to access it from the listing and click on "Report this ad".
Depending on the device that you're using, this will be just below the pictures, or on the right-hand side.
As soon as you click on "Report this ad" the tab will expand and request additional information from you.
You will need to create an account and provide additional information such as ownership of a phone number, email address, or photo.