They are not found on the site. The top-15 stats are part of a business presentation from Internet Brands, owner of the site. While not secret, I don't feel comfortable publishing the material itself. But here are the 15 busiest forums in falling order:
BA, UA, AA, DL, Premium fare deals, AC, Mariott, Hyatt, Omni, Hilton, AS, Airline Mileage programs, QR, LH, CX, Amex

At the top there is very little change year on year. At the bottom stuff happens. Climbers this year were Hilton, LH and CX