The Collaborative International Dictionary of English v.0.48:
partygoer \par"ty*go`er\ n. Someone who is attending a party[4]; as, the hall was crowded with an overflow of partygoers. [WordNet 1.5]WordNet (r) 3.0 (2006):
partygoer n 1: someone who is attending a party; "the hall was crowded with an overflow of partygoers"