"Happy birthday Liam!.... Damn our Aussie school uniforms," one remarked.
"3 years ago? That Australian sun sure does age people," joked another.
"Back when Thor was a little fella," a third penned, referring to the Marvel superhero Chris is famous for portraying.
Liam also shared his own birthday post, hinting at his tough 2020 when the global pandemic kicked off and his divorce from Miley Cyrus was finalised.
"Here’s to a better year than the last! Cheers for the birthday wishes!" he penned.
Birthday boy Liam also has another reason to celebrate - he and girlfriend Gabriella Brooks have been dating for a year.
"His relationship with Gabriella is very different from Miley. They like the same things and have the same lifestyle," an insider told E! News of the couple's "low key" romance.
"It's not a rollercoaster of highs and lows. Gabriella is very laid back and even keeled."
What's more, the entire Hemsworth clan is loving Liam's new lady.
"The family very much approves and likes having her around. They are happy for Liam that he has found someone that brings out the best in him," the source added.
The Hemsworths are currently living in Australia's celebrity capital, Byron Bay.
The famous family rung in the new year together at a space-pirate themed party hosted by Chris and wife Elsa Pataky at their mega mansion in the NSW coastal town.
Liam and Gabriella were in attendance as were eldest Hemsworth brother Luke and his wife Samantha but the famous guest list also included DJ Fisher, The Voice's Renee Bargh as well as Isla Fisher and Sacha Baron Cohen, the latter of whom recently relocated Down Under to escape Trump's America.
