"I don't want to pick out individuals, but LA is a completely different kettle of fish to Ireland," says John.
"I think a lot of girls will be in for a shock when they land.
"It's a tough business. And girls who head out there with dreams of cracking the US have a tall task on their hands.
"Unless they have built up contacts and know people in the industry, it's unlikely they'll make it. Everyone in LA is trying to 'make it' and lots of those people have spent years studying acting. They aren't just heading out for a few weeks on a whim."
It's something former actress Holly White knows all about.
Holly starred in RTE's 2008 TV documentary Hollywood Trials, which followed young actors – including Mikey Graham and Emmett Scanlan – as they tried to crack the US.
Every single contestant returned home with their hopes dashed.
Holly advises everyone heading out to plan in advance to avoid disappointment.
"Overall I've had some wonderful experiences," she told the Diary. "My advice is to go with a few other goals in mind, otherwise it will feel like a failure, which it shouldn't."
But lingerie model Tiffany Stanley is one step ahead and knows people in high places – namely, her uncle Kevin Connor.
Kevin has directed several films and TV series, including Honeymoon For One, Strawberry Summer, Chasing Leprechauns and the classic I Married Who?
"My uncle knows a lot of people in the industry," Tiffany says. "I'm staying with him and he's putting me in touch with people who organise reality castings. There is so much opportunity out there.
"I would love to present a show like E! News. I know there is a wealth of talent in LA and it's highly competitive, but I would rather have a go than have any regrets."
The bubbly model says going on her own is a plus.
"I'm going to put my best foot forward," she says.
"I'm not going over to 'make it'; I'm just going over to see what happens. I have a few shoots lined up.
"Even if nothing ever happens, it will still have been an amazing experience."