Demi Lovato, Lauren Conrad, and Rebecca Black all came out to see the pop princess in action this weekend. Find out which celeb got pulled onstage inside.
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The Nokia Theater was full of sugar and spice and stars all weekend when Katy Perry took the stage! The pop star has put on quite a show Friday and Saturday nights, and she'll finish out her run in LA with another performance tonight.

Rebecca Black (Pacific Coast News) The jam-packed arena was filled with screaming fans each night, and some of those cheering ladies were celebs! Friday night Demi Lovato came out to support her fellow singer -- armed with a Red Bull and silver face paint -- and so did Rebecca Black!

Demi tweeted about the fun evening: "SO much fun at the @katyperry concert... She's so talented. Every song is entertaining and LIVE!!" she wrote.

Black, the "Friday" YouTube sensation, probably had one of the best seats in the house and even got pulled up onstage with Perry while she sang "Last Friday Night!" The gals starred in the song's awesome music video together, so it was only fitting.

The teen star tweeted after the show: "Thank you SO much @katyperry for having me on stage tonight! What an UNBELIEVABLE experience.(: Definitely won't forget this one!!"

Saturday night reality star Lauren Conrad was spotted leaving the show in super tight leather leggings. And, no, her hair was no longer blue.

Katy's performing in LA again tonight and we imagine at least a couple celebs will be in the crowd -- if they're not already committed to attend the Teen Choice Awards this evening!