The pair touched down in Miami together on December 18, though took care to ensure they weren't pictured together – leaving the plane at different times.
CLICK ON PHOTOS TO ENLARGE
Miley recently started following Kellan on Twitter, and the pair were both at the Jingle Ball in New York at the weekend. There has been no official confirmation as to whether the pair are dating, though.
Miley has another Jingle Ball performance scheduled in Miami on Friday, but it's unclear what Kellan is doing in the city.
Since her split from fiancé Liam Hemsworth, the Wrecking Ball singer has been romantically linked to a handful of handsome young men – including Liv Tyler's ex Theo Wenner.
While she's yet to find lasting love, the 21-year-old singer says she is in a good place and has no regrets about her engagement to the Hunger Games star.
Miley with her ex fiancé Liam Hemsworth
"I don't think I realised what 19 truly is, and I got engaged at 19, and I definitely wouldn't change being engaged. It was so fun wearing a fat rock for a few years," told Barbara Walters in a chat for TV programme The 10 Most Fascinating People of 2013. "But now, I just feel like I can actually be happy."
She added: "I was so scared of ever being alone, and I think, conquering that fear, this year, was actually bigger than any other transition that I had, this entire year," she says. "I don't ever want to have to need someone again, where you feel like, without them, you can't be yourself."
Though she's clearly relishing her mew independence, the star didn't rule out getting married in the future, saying: "I think I'll want that in the time that it needs to be."