Use 'throng' to describe big crowds, emphasizing their density and number. A throng of fans waited for hours to see the movie premiere.
Pro Tip 2/3
Impersonal Feel
'Throng' doesn't indicate familiarity among the people, just their presence together. A silent throng of passersby filled the city square during the event.
Pro Tip 3/3
Slight Chaotic Sense
'Throng' often suggests a slightly chaotic or disorganized group. The festival was so popular that a throng of visitors spilled into the streets.