If you want people to add you you either need to post a link to your Facebook page or a link to your portal page.
On that page towards the top left you will see:
Pixel ID: 7288732 <-- that's mine, your number will be different!
Take that number and append it to the end of: https://portal.pixelfederation.com/en/profile
e.g. https://portal.pixelfederation.com/en/profile/7288732 to create a link to your profile on which people can click on
Remember to check back to your profile to accept friend requests (friends aren't added automatically, you have to accept). And you will get in game friends!
Remember to refresh your in game list after accepting friends on the portal
[Stickied to be linked to when people don't post correct links in add me posts]
Edited after the fact.
I'm seeing people posting add me links here (and then their own thread, or replies to other people's add me's) that haven't added me (using the link that's right up there^). If you want friends help yourself out and click on all the links you can!
Edit: Instructions in Brazilian (Portuguese I guess?) https://forum.pixelfederation.com/trainstation/d/45630-brasil-ensinando-add-amigos