Tozo
(I'm answering my own question -- in the end, I found it while browsing through a Google image search for resembles tintin sci-fi webcomic.)
Its first part, "The Public Servant" ran for 263 pages; the second part, "Empire of the Spider, had 13 pages published.
It was originally at tozocomic.com (Internet Archive link)
The new address for it is https://tozocomic.tumblr.com/
Excerpting from a 2011 io9 article on it by Lauren Davis:
“Tozo” is a Tintin-inspired retrofuturistic murder mystery
The webcomic Tozo: The Public Servant takes Hergé's visual style and transports it to a retrofuturistic universe where a murdered bureaucrat draws an earnest public servant-and his robot companion-into a web of political and religious conspiracies.
The tone for David O'Connell's Tozo is neatly set by the name of the city-state in which it is set: Nova Venezia. It's a Moebius-flavored city of grand architecture, airships (that alt-history staple), and, of course, the canals.
It's a charming mix of eras and genres with steam-powered vehicles that escape the steampunk aesthetic, a sinister figure who travels by robotic spider-legged egg chair, wisecracking miniature androids, and fatal femmes who seem borrowed from both Victorian thrillers and Indiana Jones.
...
The comic began in January of 2007, and received its most recent comic update on Sept. 22, 2014. (See Internet Archive backup.) In March, 2018 the author put up a message:
Hi Tozo readers - if you're still out there.
This website has been having some performance issues recently which have proved to be an ongoing admin headache to resolve. As my webhosting package expires at the end of March 2018, I have decided it's time to call it a day at tozocomic.com.
However, it is not the end for Tozo. The comic will be transfered to a Tumblr site, so will still be available to read. I aim to finish the transfer during March.
It's always been my intention to continue and complete Tozo's story, though personal/work committments have made this difficult. But the desire is stronger now than it has been for quite a few years, so I would urge you to keep an eye on the Tumblr site, or follow Tozo's Twitter/Facebook accounts to keep up to date, just in case...
With thanks for your patience,
David (5th Feb 2018)
Tumblr: http://tozocomic.tumblr.com (From April 2018)
Twitter: https://twitter.com/tozocomic
Facebook: https://www.facebook.com/tozocomic
When the original site's domain lapsed, the site apparently (judging from Internet got domain-squatted for a bit with some NSFW ads, leading one reader on the comic's Facebook page] to ask if the site had been hacked, to which the author replied:
TOZO Hi Michael - thanks for getting in contact. I decided to stop paying for the site and moved the comic to tumblr (http://tozocomic.tumblr.com). There was a message up on the site but you might not have seen it if you use an rss feed or something like that. Hoping to get back to updating soon.
However, the timestamps below the posts on Tumblr (March through May 2018) are not the original dates but rather when the pages were posted to Tumblr. So despite the the "May 19, 2018" date on the most recent one, there unfortunately have not yet been any new comic pages posted.
Unfortunately, I'm not sure how likely it is to resume, given the lack of updates and the fact that I might expect an author planning on resuming to pay a few dollars a year to keep the old domain, and just redirect to the Tumblr site. (That way, old links like io9's and bookmarks would still point people to the comic, and he'd have the option of rebuilding the site with a better engine.) Then again, I don't know the author's situation. (That said, at least the 263 page "The Public Servant" was finished -- I'll have to finish reading it to see what degree of closure it gives to that plot.)
