By Alexandra Ulmer

RIO DE JANEIRO (Reuters) - She has ratcheted up a million Instagram followers, exchanged tweets with reality star Kim Kardashian and been splashed on the cover of major American magazines.

Teenage gymnastics phenomenon Simone Biles has vaulted herself to stardom with her bubbly personality and savvy use of social media - all while winning gold medals with the U.S. team and in the all-around women competition.

No stranger to the limelight before the Games, the 19-year old appears to have harnessed the Olympic spotlight to become a global sporting sensation, one cute Instagram post at a time.

"'Boa noite,' or 'Good night' in Portuguese,'' she chirped recently from Rio, posting a mirror selfie with fellow all-around women's finalist Aly Raisman in USA t-shirts, Biles donning a purple head wrap and Raisman buried under a face mask.

Already touted as the greatest gymnast of all-time, firecracker Biles soars during her moves - with one, a double layout with half-twist at the end, named after her - and has smitten judges, crowds and even her rivals during jaw-dropping performances in Rio.

That awe has spilled over to social media, with the Texas-raised teenager tweeting on Wednesday that she had surpassed one million followers on photo-sharing app Instagram and thanking her fans with an ''I LOVE YALL''.

Biles has also been raking in online praise from celebrities including pop star Taylor Swift and former teen idol Zac Efron, whom the giggle-prone gymnast has said she has a crush on.

"North is watching @Simone_Biles in awe!," U.S. celebrity Kim Kardashian also tweeted recently, in reference to her three-year-old daughter with rapper Kanye West. "She's rolling around on the bed pretending to copy her lol."

Without skipping a beat, Biles tweeted back that North merely needed a Simone Biles leotard from company GK Elite to be "my mini me!"

BALANCING ACT AHEAD

Of course, once the lights go off at the Rio Games, there is no guarantee Biles will keep her spot in people's hearts.

Gymnasts burst into the public eye every four years but, as they rarely make a splash at two successive Olympics, their stardom sometimes fades quickly.

The experience of U.S. team mate Gabby Douglas, who won the all-around women's gymnastics event at the 2012 London Games, suggests it is tricky to balance the surge in attention with intensive training.

After London, Douglas took a two-year break, starred in a reality TV show and switched coaches several times. She was shaky at U.S. trials in July and there was concern she wouldn't pull through in Rio although she has so far performed strongly.

Biles' supreme talent and work ethic may make her road ahead smoother.

In any case her compelling life story has already turned her into a media darling.

At the age of three, Biles was adopted by her grandfather and his wife because her biological mother battled alcohol and drug addiction and was unable to look after her.

The stability that her adoptive parents Nellie and Ron offered included enrolling Simone into a tumbling program in Texas after a daycare field trip to a gym -- a decision that eventually turned her into a 10-time world champion.

Swamped by camera crews and microphones after her triumph on Thursday, Biles distanced herself from the shining lights.

"I'm not a celebrity, I'm still just Simone," the 1.45-metre Biles told reporters. "But it's amazing to be recognized for all the success me and Team USA has had over these Games."

(Reporting by Alexandra Ulmer; Additional reporting by Pritha Sarkar; Editing by Frank Pingue)