Glee co-stars Monteith and Rivera hosted the New York leg of the awards ceremony and decided to turn up the heat by promising a steamy smooch with each of the highest bidders.
Former E.R. star Stamos sparked a bidding war for Monteith before deciding to enter the auction himself and pucker up for his own charity kiss.
Stamos was in for a surprise when his winning bidder turned out to be a male fan - but the actor brushed off the same-sex smooch and joked, "I got the better prize. Come to daddy!", before leaning in for a quick kiss.
Monteith ended up getting intimate with Smash star Megan Hilty, while Rivera's big spender dipped her low as they locked lips onstage.
The trio's fun antics each drew bids of $5,000 (£3,125) for the GLAAD cause, which was also attended by movie producer Harvey Weinstein, rap mogul Russell Simmons and actress Dakota Fanning.