Singer Katy Perry and her rumored beau John Mayer dressed up in ghoulish costumes on Friday (19Oct12) for a star-studded party to mark her upcoming birthday.

The I Kissed a Girl hitmaker, who will turn 28 on Thursday (25Oct12), donned sharp fangs, a velvet cape and red-colored contact lenses to transform into a vampire, and Mayer showed up with a prosthetic nose and chin for his zombie hunter outfit.

The bash, held at The Magic Castle in Los Angeles, was also attended by Twilight's Kristen Stewart, Perry's brother David Hudson, her stylist Johnny Wujek, actor Matt Dallas, and Raising Hope star Shannon Woodward.

Perry posed for photos with Mayer, and also took to her Twitter.com page to politely decline gifts from friends and fans, asking instead for donations to filmmaker David Lynch's meditation charity.

She writes, "Transcendental meditation changed my life. For my birthday I would love to pay it forward. In lieu of gifts, donate (to the David Lynch Foundation)... Your donation is not only special to me, but to all of the people whose lives you will help through the lifelong gift of meditation."

It's the second birthday Perry has celebrated this week - on Tuesday (16Oct12), she enjoyed a more low-key dinner date with Mayer in New York City as he turned 35.