That's wrong. Moore scholars point to the two page feature he wrote on The Shadow, published in the fanzine Seminar #2 in September 1970. Two copies sold on eBay for £350 in 2009.
But it turns out that wasn't his first, either,
His first work was published four months earlier, and created the year before that when Moore was fifteen. An article in the first issue of Utopia/Valhalla about HP Lovecraft.
"He was the last of the great horror writers. Some say, the greatest."
And a copy went on eBay, and quickly rose to £3000 or $5100. The article is described as,
The article is essentially a short biography of Lovecraft; a writer Moore has referenced through much of his career including some very recent work. The editor (Paul McCartney) writes that the feature was to be accompanied by three of Moore's drawings too (which are named) but were going to be held off for issue no.2 (which was certainly never published).
The previous record for an Alan Moore article was Outbreak Of Violets, given away at an MTV Awards do, and getting £700 on eBay when it sells. But that was also accompanied by the great and good of comic book artistst and illustrators. This has far outmatched that.
There are no other known copies of Utopia/Valhalla #1 in existence. There were also no further issues. Unless you know of any… the fanzine in question also contains,
Stan Nicholls, Wonder Woman, Western Comics, Steve Moore, Heroes Unlimited & other fanzines, Pre-decimal comic adverts including "This Month's Special Feature: Blackhawk", Ron Bennett etc
Front & back covers by Alan Hunter
Let the hunt begin…