To search for a player in the Company of Heroes 2 ladders, you must know either their Steam ID #, or the name that they use to log in to their Steam account. Searching via "alias" (display name) is not yet available.
You can use the Steam WebApp to search for a player by "alias" (display name). When you find the player, copy their Steam ID number from the url. For example, Ami's steam profile page url is:
Find his Player Card by entering "76561197993926044" in the SteamID search box. Our "SteamName" search box is primarily for you to search for yourself, as that login name is normally hidden from other players.
If a player has hidden their ID # with a custom URL, you may have to use a 3rd-party Steam ID converter app to track them down.
Another option is to find the player in a game in the replay section, and click through to their Player Card.