Assuming you're writing to a celeb via their agent, then you start the letter with "Dear celeb's name", your letter is to the celeb, not the agent.

[quote="The.Evening.Optimist"][color=#BF0000]'Dear Sir/Madam' - address it to the agent as there's only a handful of celebrities in the world who read their own fanmail. :) [/color][/quote]
I have to say I think the opposite, most of them are really busy to be a celebrity, they usally have a sectrey who does there danmail (prepares item for them to autograph). But otherwise you do write it to the actor.
jason ;-)

[color=#BF0000]'Dear Sir/Madam' - address it to the agent as there's only a handful of celebrities in the world who read their own fanmail. :) [/color]

When writing to an agent...

do you start the letter with Dear Sir/Madam or Dear (celebrity name)

Thanks