Any way to easily find someone on Steam client?

If you know their email address or steam name go to the steam app > friends > add a friend and search there.

"Enter the player name, account name, real name, email address or profile url of the person you're looking for."

If you don't have any of that information, then no, there is not an easier method.

Edit: Unless you know the person is on one of your friends friends list! (In which case, search their profile)

Well, real name worked, I thought I tried that but guess I didn't. I was having a hard time finding a winner of one of my giveaways. Thank you.

steams wierd like that, just search their full name, or account, email whatever :p

searching someones username(name they registered with and use to log in) it will only come up with them even if they changed it)