See what Hollywood's biggest celebrities were up to this week.

- John Mayer and Katy Perry celebrated the release of her new single, Roar, at Manhattan restaurant, The Lion, on Monday night. Just as Perry and her 15 friends finished dinner in a private part of the restaurant, Rihanna arrived at the swanky spot to join the crew.

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- Real Housewives of Miami's Adriana De Moura and Fox News Magazine Dating Columnist and Maxim Model, Diana Falzone were spotted at Swoon & The Daily Summer's Luxury Cover Party. At the invite only bash, guests enjoyed custom cocktails, taking fun and flirty Swoon photos in the Bosco Booth, and mingling with VIP guests at Georgica in the Hamptons.

- Dane Cook took a break from stand up to serve as Nascar Grand Marshall at the GoBowling.com 400 at Pocono Raceway.

- Brooke Burke and her daughters were spotted snacking on popchips at The Young Fabulous and Broke Mini Launch Party in Malibu this past weekend.

- Jax and Stassi, stars of Bravo's Vanderpump Rules, visited VISTA Lounge for a quick drink under the stars Friday night after their Reality Check event at Mohegan Sun.

- As part of Renaissance Hotel's new digital program, Discovery Doors, singer CeeLo Green surprised some lucky hotel guests in New York. A grandmother, mother and daughter were in awe when they opened their hotel door and found CeeLo serenading them on the couch with candles and rose pedals. (Watch the video below.)