If your webpage ranked in Google, and now it no longer ranks, then yes, maybe you have been penalized by Google.
First, though, a common misconception is that many webmasters often mistake a penalty for a simple algorithmic change. It’s widely known that Google updates its search algorithm routinely if not daily so it’s more than conceivable that what once worked in your favor now no longer does simply because their filters were adjusted.
So expect to see some daily fluctuation in the rankings, especially if you have a young site.
That said, if you didn’t fully follow Google’s guidelines you could get hit by a penalty. To see if you did, just type in “site:yourdomain.tld” and if nothing surfaces then indeed, you’ve been banned from their index and you’ll have to take the proper steps and then file a reconsideration request.
On the other hand, if your site does show for the above query, but no longer when you type “yourdomain.tld” into the search, then again you my be penalized especially if your domain name is not a common phrase or keyword.
As for penalties, they exist. -950, -30, -60 penalties. Over-optimization, link schemes, duplication and the list goes on and on for ways to get on Google’s bad side. And the list change every day, with some dropping off the list as new ones get added.
If you do get penalized – that is you find all your important keywords suddenly depressed by a similar mark in the rankings – then take a cold hard look at your site to see what may have caused the drop. Or even better have someone else look at it. The fine-toothed comb is your friend and that’s the place to start.
The good news is often you will find something – maybe some bad links, maybe you got hacked, etc. – and Google will reinstate you.