The event was thrown at the Los Angeles home of Balthazar and Rosetta Getty and was attended by close friends of Van Der Beek, reports People.
"The party was very small and intimate," a source said.
"Ashton and Demi looked happy and totally unaffected by recent relationship rumours. James and Kim were glowing. Despite being about to burst, Kim looked amazing."
Van Der Beek and Brook married in August.