Chace Crawford's old high school and college friends - 15 of them! - helped the Gossip Girl star celebrate his 24th birthday this past weekend.

New friends, such as co-star Sebastian Stan and actor Toby Hemingway, also partook in the festivities as the Texas native partied in New York.

"His hometown friends got along great with all his New York city pals," a source tells People magazine of that publication's hottest bachelor.

The whole gang then flew from the city out to Watermill, New York, where they stayed at some private digs for the weekend-long bash.

"It was the best birthday Chace ever had because he was amongst his closest friends," says the source of the Gossip Girl cast member.

The group barbequed, ate, drank and were treated to meals cooked by a private chef. They also played games and went swimming.

But it wasn't all chilling on the sand: To raise the excitement level a bit, they chartered a speed boat and went out in kayaks.

And in honor of Chace Crawford's birthday on Saturday night, "They, of course, sang 'Happy Birthday,'" says the source.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.