Steam is a place where many hacks happen from time to time, and many accounts are also stolen. It's one of the biggest gaming platforms and so it's unfortunately true that many players lose their accounts, even with email.
Many players have lost their account this way and didn't even try to get it back because they didn't know how to do it. However, in the past years it was much easier as the gaming industry was not so huge and Steam support did not have so many requests.
Now it's a bit harder though, and if you want to get your account back it's best to try to remember how you paid for some games and various other information that no one else could know about you.
But if you don't have an email and it was stolen you also need to contact Steam support via any other email and they will try to help you as quickly as they can.Access to Email
That being said if you still have access to email try requesting a password change and thus logging out your account from all devices where it was logged in. Change your password and try logging into your account.
If you do log in you need to change your password to your email as well and preferably to a completely different one.But if you don't log in, or you don't get any email about changing your password, read on.Without Access to Email
However, if you no longer have access to your Email or your Steam Account Email has been changed, please contact Steam Support from any email as soon as possible. The more information you have the quicker Support will deal with your request and they may ask for some additional information.
Steam Support is the last resort since you are talking to the person who works there and is the only one who can help you. So even if Steam Support tells you there's nothing they can do, you'll probably never get your account.
That's why we recommend making Steam Guard and having completely different passwords for your Email and Steam. The more complex the better, or you can use one of the password managers which are also really reliable.
Protect your account as best you can and you should never lose it. And this is also true on Email and others where you have to log in with a password. Steam Support should always help you though, the most important thing is to prove to them that you are the true owner of the account and that someone has tried to steal or rob you.