Before making a comment on this page: AccountKiller DOES NOT (and CANNOT and IS NOT ALLOWED to) delete accounts in your name. You should do this yourself.
Their terms state: "You may terminate your membership at any time, for any reason by following the instructions on the Resign pages in Account Settings, or upon receipt by CitySex of your written or email notice of termination."
However, 'resign' never appears on the Settings page, perhaps this only goes for paying members (which we are not, obviously ;)). So instead: (1) be logged in on the site, (2) click the link to go to the support section. (3) Scroll down for the webform, you'll see it under How can I contact customer support, then click Contact Support form. There, request deletion using the form.
Direct removal link: http://www.citysex.com/#support
If you can't find any contact info and still wish to ask something, for example a question about what exactly is deleted, about data retention, etc., you may contact the domain owners using this info.