More important(ly), can you help us find XXXXX?I'd long ago been taught that's a ly-free zone, with "importantly" being reserved as an adverb to describe to describe an action; for example, "The judge strode importantly to the bench." With a bit of nagging doubt in my head, I did a bit of research to ensure I wasn't wrong.
As it turns out, it's a bit of a sister-kiss: Either one is acceptable usage according to Merriam-Webster's and other authorities, though my web search indicated a slight lean toward "more important." The reasoning is that it's not modifying a verb, it's modifying the entire phrase that follows it--you could think of it as "[What is] more important, can you help us..."
Alas, as with all grammar minutia, whichever way you write it, a stickler on the other side will read it and think "AHA! You big dummy!"...forgetting that it doesn't mean a darn thing in the ability to convey or understand the message. I am reminded of the big-endian vs. small-endian argument among the Lilliputians in Gulliver's Travels. Eat your softboiled egg any way you please.
UPDATED: While we're on the subject, Yolander Prinzel of Freelance Writerville alerted me to "Error Proof: How to defend yourself from grammar pedants" from the October 4, 2009, New York Times Magazine. Clever stuff.