Sad, but it's possible, thanks to javascript..
I got the index page from your server and analyse it. You have malicious code in your page. I guess someone create an account in your dating application and write the following javascript code to redirect page to datetopia.com
Code:
<script>document.location='http://www.datetopia.com';</script>
It's a very bad and shame attitude of course... I think the guilty user has userid = 12, but maybe he created more users like that...
Anyway remove the user 12 and see if that works.
And you'll have to fix your script : forbid any html code from the user in the inputs.
Hope that helps,
David.