Go to the Temple of Mara in Riften. Speak to the guy with the hood. You'll be able to buy an Amulet of Mara from him. Wear it around and if you see anybody else wearing one, talk to them. You might have to do a quest for them, but you should be given the option of "Interested are you?" Choose that and baddabing. If the guy isn't in the Temple, try the Bee and Barb.