Good looking salmon! Did your plank smolder? I can't tell from the picture.
I've done cedar planked salmon a few times on my Weber Genesis (gas). I place the plank directly over the flame and wait till the plank begins to smolder before placing the salmon on it, skin side down. I'm usually successful in preventing the plank from actually catching fire.
I lose the skin that way, but the flavor of the cedar smoke really complements the salmon.
What did you use for a plank? I've seen them for sale specifically for planking, but they seem pretty expensive. I buy cedar fence pickets at the local big box hardware store and cut them down to size to fit my salmon. Results are always good-tasting, but I suppose I should cross my fingers and hope there's nothing nasty in the pickets!