Miley Cyrus 18th BirthdayMiley Cyrus was days shy of her 18th birthday over the weekend, but that didn't stop her from celebrating like crazy. The onetime 'Hannah Montana' star told Access Hollywood she's dedicating an entire month to the festivities, which began at LA hotspot Trousdale on Sunday night.

The party was a star-studded affair, with guests including Kelly Osbourne, Demi Moore, Ashton Kutcher, Mark Salling, Chord Overstreet, and Rumer Willis.

Cyrus was allegedly spotted smooching Nickelodeon star Avan Jogia later that night. Although she seemed hot and heavy with the 'Victorious' star at her party, a source tells PEOPLE, "She's still single... [they] are getting to know each other."

Take a closer look at TMZ's photo of the steamy kiss on the neck and gauge for yourself...

A source told Page Six Miley's camp is wondering who leaked the photo. "Only her closest friends were there, so there have been questions asked about how these pictures got out. She's telling people it looks a lot more intense than it actually was."