https://support.steampowered.com/
Create new account, separated to your Steam account (it won't work with your main Steam account), then go to
https://support.steampowered.com/newticket.php
Create a new ticket, fill it with:
It's up to you to type what's the ticket (That huge form space on the left), an example would be:
Filling out
Hello, my Steam account has been hijacked as of [day/month/2011 (31 July 2011?)] and the hijacker changed most of the account details, and removed all of the friends.
Proff of ownership comes from IP and provided CD Key, if you'd like, check the IP logs on my Steam account, and then, if possible, revert the account to a previous state, perhaps since [insert a day before your account was hijacked (30 July 2011?)] so I also get my friends back.
Thanks anticipated, I hope this will be solved soon.
Well I think I missed or mislead some stuff there, it's up to you what to put between the "[]", don't mention anything about receipt, maybe you'll be luckier and won't ask you for it.
It's recommended to make this ticket from another computer than the one your computer was hijacked, seeing if the hijacking was done through a keylogger or some sort, you will encounter bigger problems, seeing the hijacker can see the stuff you filled in, and eventually do the same himself later on to "receive back his stolen account", permanently.
