Bruna and Neymar: They met in the end of 2012 or beginning of 2013 through friends and started dating in January. In February, their relationship became public during carnival and they confirmed that they are together since one month.
Shakira and Gerard Pique: Shakira song the official song for the World Cup 2010 and some footballers appeared in the video for Waka Waka. One of them was Gerard and he met Shakira at filming this video.
Melissa and Marc: There are two different stories on how they met: They either met through Coral (Melissa and her are friends) and Sergi (Marc and him are friends) or they met trough Melissa’s work. She is a journalist for MotoGP and Marc is a big fan of it.
Raquel and Ivan Rakitic: She worked in a café near his hotel in Sevilla but it took some month until they went out together.
Nuria and Xavi: They know each other since childhood but started dating much years later.
Coral Simanovich and Sergi: One of Coral’s Instagram pictures appeared on the popular page. Sergi liked it and then they started messaging and phoning each other.
Anna and Andres Iniesta: They met at holidays in 2007.
Carolina and Pedro met when he was 17 and she was 22 years old in Barcelona.
Olivia and Alex Song: They met in their childhood.
Carla and Claudio Bravo met when they were teenagers at school.
Antonela and Lionel Messi: They know each other since they were five years old. They met through Antonelas cousin who was Lionels best friend.
Sofia and Luis Suarez: They met when he was 15 and she was 13 in their hometown in Uruguay.
Sophie and Jeremy Mathieu: They met in a club through Jeremys brother. Sophie and him were friends.
I am not sure about the other wags but I guess most of them met through friends. If anyone knows something more, please write me and I will add it.