1. You write the address similarly:
(If to a theatre, you're not specifc; So to a Theatre star) :
Natalie Toro
c/o Al Hirschfeld Theatre
3457867565876
New York, NY 10036
USA
(Not currently playing yet..!)
or
2. TO a band or singer or something:
Augustana
c/o Paradise Rock Cafe
kgfjg87
Boston, MA
USA
(If you're writing to one band memmber, such as Dan Layus write:
Dan Layus
Augustana
c/o Para....)
To get the address, use this forum under "Request Via Venue Address" or find out when they're playing atleast a week in advanced.
Search the celebrity(ies) past feedback for via venue. If it looks like they respond on the road, then send a picture or soemthing. There are plenty of other ideas, just check out the Via Venue Feedback subforum. If it looks like it takes a while to respond, press your luck and just a letter.
If sending to a theatre person, they'll most likely have their own photos or playbills; but I've yet to have a personal success from a band.
Good Luck! ANd search this forum, this is a question that's asked allllllllllll the time.