Firstly, if you could open your Steam browser, on the top you'll see an option called View - hit that and then servers. Once you hit servers, a new box will open and there's a filter button at the bottom. Ensure that ARK is being filtered, then it should hopefully load a list of ARK servers. See if you can connect that way.
Another option is to use this fan-made website. You just click on the server's IP that you'd like to join and then it should launch the client via Steam. Might not work on all browsers though. Mind you, I manage fine on Chrome with it. http://arkservers.net/ or http://arkserverlist.com/
Another issue could be that you've updated the client and that particular server may not have updated, therefore you're unable to find it because you're on two different versions.
Firstly, if you could open your Steam browser, on the top you'll see an option called View - hit that and then servers. Once you hit servers, a new box will open and there's a filter button at the bottom. Ensure that ARK is being filtered, then it should hopefully load a list of ARK servers. See if you can connect that way.
Another option is to use this fan-made website. You just click on the server's IP that you'd like to join and then it should launch the client via Steam. Might not work on all browsers though. Mind you, I manage fine on Chrome with it. http://arkservers.net/ or http://arkserverlist.com/
Another issue could be that you've updated the client and that particular server may not have updated, therefore you're unable to find it because you're on two different versions.