The sandy soiree was held inside tents on the Malibu shore -- about 20 miles away from the Beverly Hills zip code made famous by the original series, which ran on Fox from 1990 to 2000.
Original series stars Doherty and Garth, who will reprise their roles as Brenda Walsh and Kelly Taylor in the new show, arrived separately.
Joe E. Tata, who will return as Peach Pit cafe owner Nat, also attended. All three posed for photos with partygoers.
However, it was the new cast members who seemed to be having the most fun. Tristan Wilds, who stars as recent Beverly Hills transplant Dixon Wilson, and Dustin Milligan, who plays popular jock Ethan Ward, chatted at the party's meat carving station. Lori Loughlin, who portrays Wilson's mother Debbie, and Jessica Walter, who plays Debbie's mother Tabitha, mingled at the noddle bar.
The premiere episode was not screened during the fete. In an unusual move, CW recently announced pre-broadcast copies of the series would not be distributed to TV reviewers and reporters.
The CW said the lack of preview footage represents a "strategic marketing decision" by it and studio partner CBS Paramount Network Television. The new "90210" is slated to premiere Sept 2.