How do I report a hacker?

[Somniator]

Here's the story. I was checking my e-mail and it said someone accessed my account. I then looked at my CSGO inventory and $20 worth of skins were gone. It said I "traded" with some guy named Dominik. I never knew the guy so he must've hacked my account. How do I report him and get my stuff back? (I have a screenshot of the "trade" if that helps.)

[Cathulhu]

Regaining access to your lost Steam Account and resetting your account credentials (Link)

[Tev]

Read: https://support.steampowered.com/kb_article.php?ref=1266-OAFV-8478

Secure your computer
[/h1]
Scan the computer with an antivirus* & antimalware scan in safemode 
First download & install Malwarebytes' Anti-Malware at http://downloads.malwarebytes.org/file/mbam/
After that restart your computer
During the time the computer is still booting up, tap F8 until you get to this menu[pad3.whstatic.com] <- clickable.
Choose Safe Mode.
Perform your antivirus & antimalware scans (with the rootkit scan ticked.)
Restart your computer.
 * = If you can do a bootscan with your antivirus, do it.
Change your passwords
[/h1]
Create a ticket
[/h1]
Register a Steam Support account at https://support.steampowered.com/register.php
Create a Steam Support ticket at https://support.steampowered.com/newticket.php
What product are you having an issue with?
Steam
What type of problem are you having?
Steam Trading/In-Game Items
Stolen/Hijacked Items
Include Proof of Ownership: 
https://support.steampowered.com/kb_article.php?ref=2268-EAFZ-9762

Returning items that were taken while the account was hijacked is handled on a case-by-case basis
Inventory restorations are granted on a case by case basis. In order for Steam Support to restore items, technicians will need to verify, using Steam’s internal data, that the account was hijacked.

Your account must meet the following criteria in order to be considered for an inventory restoration:

The account data must indicate that the account was hijacked
The owner of the account has never received an item restoration in the past (item restoration is a one-time gesture per user)
The items were removed from the account within 30 days of submitting a Steam Support ticket
Trade confirmation was enabled on the account at the time of the hijacking
The account has reliable data (trade restoration may be denied if an account appears to have poor data due to proxy/VPN or public computer use, abuse reports, trades with hijacker or scammer accounts, or any other data point that is a concern to Steam Support Technicians).
If your items were traded away or sold on the marketplace by an account hijacker, submit a Steam Support ticket with your report.

Ensure that your report contains screenshots of the trades or Market sales in question, as shown here: Listing Trades for Steam Support. Note that any attempt to mislead Steam Support will cause appropriate restrictions to be applied to your accounts.

For information on how to safeguard your account, please read our Account Security Recommendations and Account Phishing FAQs.

[luciiiii._. (ESP)]

.-.