TORONTO -- Julia Roberts stepped out of the elevator of her hotel during the Toronto International Film Festival this past weekend and finally spotted it -- a giant photo of herself flashing her megawatt smile on a lobby wall.

The four-time Oscar-nominated star had heard about the artwork from others but didn't see it for herself until Saturday, and she knew exactly how to immortalize the experience: With a post on her Instagram account.

"I just started laughing and I said, 'Please, somebody take a picture of me in front of this picture, because it's massive and hilarious and I might give it to my husband for Christmas,"' Roberts said with a laugh in an interview at the festival, where she is starring in the film "Ben is Back" and the Amazon series "Homecoming."

Roberts is a part of a growing group of stars who once enjoyed relative anonymity on social media but are now joining the ranks of influencers and opening up their private lives on Instagram.

Other A-listers who've launched accounts on the social media platform in recent months include Natalie Portman, Tom Cruise, Nicole Kidman, Jennifer Garner, and Michael J. Fox.

"I was told to join instead of being asked if I wanted to join, to be honest. It wasn't something I was looking to do," Garner, who joined Instagram in September 2017, said in a recent interview for her new action film "Peppermint."

Garner initially worried about the move, thinking, "'Nobody needs to see how boring my life is,"' she said.

But once she figured out her Instagram voice, she found the fun in it.

"I really enjoy finding a way to connect and let them in and be a part of their lives as well and hear what they have to say and start conversations," Garner said.

Roberts said she, too, initially found it "very stressful" to post.

"I just thought, 'What am I supposed to do? I don't even know what to do. I'm terrible at taking pictures of myself, I feel like a jackass, as frankly, any decent person should.' I just felt so silly," Roberts said.

Some people had suggested the former "Pretty Woman" and "Erin Brockovich" star use the app as a way to promote her work, but she wanted her account to be more than that.

Like Garner, she's now finding the humour in it. And she likes the idea of being able to see what friends are up to.

"And I find that it makes me look forward to working, because then I go, 'Oh, then I have something legitimate to post and not just "Here I am making cookies,""' Roberts said.

"But you have to find a sense of humour and I think that the benefit I've gotten from it, truly, is the tiniest little insight into what it must be like to be a teenager in this day and age.

"As the parent of teenagers, I'm finding it very informative and interesting and empowering in that regard, where I have a little glimpse into what the youth of our society participate in and the positives of it and the frustrations of it."

Canadian actress Evangeline Lilly, said she joined Instagram several years ago as part of her job and "went into it very reluctantly."

"As a staunch Generation X-er, I thought social media was destroying the world and I was very reticent to be a part of it," said the star of "Ant-Man and The Wasp."

But her manager pointed out that being on social media would help her promote her book series, reach her fans directly, and bring attention to social issues she's passionate about.

She also liked that she could have more control over how her voice got out into the world after some frustrating experiences of being misquoted.

"I had reached a point of such intense frustration, I was telling my manager, 'I never want to do press again,"' Lilly said.

"And he was like, 'Well that's not the answer. But maybe if you had an outlet to be your own voice in the world, then when someone else got your voice wrong, then maybe you could live with that a little more knowing that you could correct it."'