Never. But then again I dont do the whole 'miss you' crap too. I'm not very expressive. People say these things so often to every person passing by it doesn't really mean anything. A friend use to always write 'miss you xxx' in texts, I'd find it so awkward because I'd forcefully have to say it back. When in fact in reality I forgot this persons existence till they'd text lol.
The last time i sincerely said "i love you" was 2 weeks ago, when my sister dropped a box of lindors on me... other than those occasions i rarely ever say it.