Organize to meet and ultimately have sex with, especially via an online social network like twitter or facebook.
"P" here may directly refer to the English word "pander" or the slang "prakatatumba" but it also indirectly refers to the penis or the pu**y, so the slang is gender inspecific.
Often used in any of these forms, "Setting P", "Set P", "Set the P", "Set that P", "Set my P" etc.
Chris: Janet is so freaking hot. I visit her facebook page every day to jerk off at her pictures.
John: If you like her so bad and she's that hot, set that P!
Anne: It's almost vals day and no one has offered to set P. FML.