What should i do if i've touched someone who may have been exposed to ringworm?

Stop worrying: Ringworm is easily treated. It's usually not even transmitted by touch -- nobody knows how it gets started. Truth be told, I think you're over-concerned about infection -- it's good you want to guard your health, but ringworm is utterly trivial, serious infections of any sort are almost never transmitted by mere touch. Life's hard enough without troubling yourself over this. Best wishes.

Wash. Ring Worm: Ringworm is a common fungal skin infection otherwise known as tinea. Ringworm most commonly affects the skin on the body (tinea corporis), the scalp (tinea capitis), the feet (tinea pedis, or athlete's foot), or the groin (tinea cruris, or jock itch). http://www.webmd.com/skin-problems-and-treatments/ss/slideshow-ringworm