At the moment, you cannot type an emoji into the search box in order to search for people using that emoji.
1. You can't search by when a specific emoji was used. I can't do a search for :wink: since it just brings up the actual word "wink" instead of the emoticon emoji
2. searching by the actual ASCII character (on windows use Windows+; or copy a discord emoji after sending it with a \ before it) returns no results
There's also a bit of a bug if you accidentally try.
You can't delete ASCII emojis once typed in the search bar. Can't Ctrl+X, backspace, or delete them. That's just a general bug. You can close the search and they'll be gone when reopened. That's the only way to delete them atm.