I have found many websites, (like https://moviepilot.com/hashtags/AvatarTheLastAirbender) about there being a sequel to the fantasy film Last Airbender, but I can't find any release date. Can someone help? I'm not sure if any of these sites are solid sources.
Wikipedia is usually a pretty good first place to check.
It currently says that M. Night Shyamalan’s last word on the subject was in a 2015 interview with UK newspaper The Metro, where he said an Airbender sequel wouldn’t be his next project (after 2015’s The Visit).
He’s since made Split, and has committed to making a sequel to it, Glass, scheduled for release in January 2019. So if an Airbender sequel depends on him (which, surprisingly, it might do?), presumably it’ll be a while away yet.
Googling for "announced" and "release date" along with "Last Airbender 2" does indeed throw up a few articles that seem to assert that a sequel has been “confirmed”, but none of them feature any quotes from Shyamalan, or anyone at Paramount, confirming a sequel; nor do they link to any articles that do.
I’d rather not link to them, as it seems like they’re intentionally writing misleading headlines and crappy articles in an attempt to attract traffic from enthusiastic fans like yourself. But I’d suggest you ignore vcpost.com, movienewsguide.com and thebitbag.com in future, and stick to publications that report actual things that happen.
The site you linked to, moviepilot.com, does have a really good summary of statements made regarding a sequel — none of which are commitments to actually making one.