Here we have a link
http://www.playframework.org/documentation/1.0.1/ide
about how to configure playframework to be working with different IDEs. There they
If its a play project, from the command line :
play debug
If its a SBT play project from the command line :
sbt -jvm-debug 9999 run
debug port is 9999 by default
now create a remote configuration
in IntelliJ :
Go to "edit run configurations"

Create a new remote configuration (port 9999, all other details leave with default values)

run the new debug configuration (don't forget to put a break point)