In a way, there is. There is no "search" button, but there is a way of doing it:
http://armorgames.com/user/
Then put the user's name after the last slash. This only works if you know the exact name of the user, though, so if someone has a complex number in their name or a weird spelling that you can't remember, you'll just have to wait until they pop up again.
If you know the person from somewhere else but you don't know their AG username, ask them from the place you know them from, whether it's real life or a different site.
