Then what you do is put someone's name after the "/user/". For example, if you were searching for me, you would put /user/Owen135731, and it would bring you to me.
If you are looking for random people, there's no specific way to do it. Just go on the forums, find people, and talk...
There isn't an official user searcher in this website, so if you need to find someone(and you do know there username), type they're username after this /user/ on this url : www.armorgames.com/user/
If you we're actually asking, how to find a user with a search box. There isn't a username search box, but it would be a brilliant idea to implement that to Armor Games 3.0.
There is no proper AG search because it would be too broad (Everywhere where the user has posted would pop up). It's the same reason the Community search was taken down.