I belong to the Northwest Playwrights Guild, with chapters in Oregon and Washington. On-line Information about plays, playwrights, playwriting, writing groups and theatres is available on line. Some colleges have theatre departments. Some colleges occasionally offer students opportunities for staged readings. Classes are also a good way to meet other playwrights and theatre people in your community.
Some theatres offer classes in writing for the theatre.
These classes can be a wonderful opportunity to become part of a particular theatre community. Because producing a play is a community effort, for some playwrights becoming part of that community is part of writing for theatre. Other writers prefer the more solitary writing life. While you should choose the path more comfortable for you, at least be aware that there can be more to getting a play produced than writing them and mailing them off to theatres. A Complete Business Guide for Playwrights, Composers, Lyricists and Librettists.