Don't write one, unless it's heartfelt, handwritten, and is actually a thank you note. This is in contrast to a typed form letter where you give the interviewer thanks and then proceed to spend the rest of the letter talking about why you're good for their school.
I never wrote them to interviewers, and I did fine in the admissions game. Now that I'm a student, I see how others around me feel about "let me into your school" letters. These letters written to interviewers WILL NOT go into your file here and WILL NOT have any bearing on your decision. Actually, they do go into a file, but said file is in my bedroom
