Just go out and say it. Ask them out for a cup of coffee and tell them what you appreciate about them.

✫ They're a hard worker

✫ They effectively motivate other people

✫ They're easy to coach

✫ They're disciplined or go the extra mile

✫ They always cheer you up, etc.

Don't mince words just tell them straight out. An employee who knows just how much they are appreciated will work harder, enjoy what they do more, and pass that psychic happiness along to other employees.