They usually work in Plaza Laureles, right across from the Cathedral. They aren't exactly mimes, though they keep silent and often paint their faces white. And they aren't really clowns, but they will crack you up--no Spanish required, they are a universal idiom. The are also interactive artists that use strangers as their medium, psychologically controlling people and manipulating into entertaining others--often in spite of themselves. Those who refuse to participate in the papaso's schemes quickly become tools for merriment and even shy girls get dragged out to perform.
A warning: foreigners, particularly gringos, are ripe targets for tormenting, so keep a low profile. But if some maniac bores through the crowd to get you out there for some diverting entertainment, you best go along with the show.
It's an art form that you see around Mexico's larger cities, there's even an academy. Here's what: the 'payaso' (clown) gathers a crowd, mostly just be being there with a white face, maybe a tuxedo or something, and blowing a whistle or horn, or just cutting up. As the crowd gathers, the payaso may do some mime stuff, generally mocking the crowd. Then he moves into serious, one-on-one mocking. He will select people from the audience to come out and participate, often just dragging them out in spite of protests. Pretty young girls are popular, macho guys, anybody the honed instincts of the payaso thinks can be used to make funny. Once a troupe of innocents is assembled, ususally 4 or 6 people, half of each gender, the routine consists mostly of modeling behavior, such as flirting with others, browbeating the subjects into copying the payaso's behavior, then making fun of their performance, all without words, but with a find command of gestures, whistles, and expressions. As the victims get used to their status, or start hamming it up, the behavior gets a little wilder--I once had a payaso snatch a blushing young girl up and toss her into my arms. Looking up at the bearded face of an older gringo in whose arms she was helpless caused her to do some pretty priceless facial antics. The crowd just loved it. I didn't want to be there in the first place, The girl was mortified--but went home a hero with her buddies.
It's really a scream, and the people are the stars of it all, directed by the machiavellian payaso--whose payoff comes at the end with a passed hat. It's a pretty painless way to get into show business.