Down syndrome teen 'couldn't stop smiling' after Kiwi stars help make him a birthday video

A teenager with Down syndrome has been wished Happy Birthday by a star-studded lineup thanks to a heartwarming video created by his carer.

Kaitlyn Amanda, 21, harnessed the power of social media to ask well-known New Zealanders for photos of themselves holding up signs saying "Happy 17th Birthday Josh".

And the response she got back was priceless, with photos and videos sent in from dozens of celebrities - among them singers Lorde and Guy Sebastian, media personalities including Hilary Barry and Jono & Ben, and athletes including Valerie Adams, Liam Malone and Malakai Fekitoa.

Even erstwhile Bachelor Zac Franich wished Josh a happy 17th, while Tania Dawson, aka Miss Universe New Zealand, told him in a video she hopes he gets "everything your heart desires".

Amanda told 1 NEWS after almost four years she would soon have to end her role as Josh's part-time carer.

"It's the last year that I'm going to be with him, and I wanted to try do something special for his birthday. He never wants anything," she said.

In a Facebook post she thanked all those who pulled together to create the video and to contact Josh's favourite stars.

"You guys made this happen! Josh is one lucky boy! Thank you NZ."

Amanda told 1 NEWS Josh "couldn't stop smiling" after his mum showed him the video this morning.

In a response on Facebook Josh thanked "everyone who made a video for me" - ending his message saying "I love you all" and blowing a kiss to the camera.