Facebook, have I been blocked or have the deleted the account/changed privacy?

Basically, I cannot find this friend anywhere, I type in their name on the general top search bar - nothing, I look through my friend list - nothing, I look through mutual friends friend lists - nothing, ever logging out and using facebook on my girlfriends profile, I can't find them. Or just typing them into google, and not logging into facebook at all.

However, in my chat box, I see the persons name, but instead of a profile photo, there's just the blank white one FB has as standard -


I've erased names and crossed out pics for obvious reasons.

Have they deleted their account or simply changed their privacy setting to themselves, whenever I click on this persons name through chat I get this message

"You may have clicked an expired link or mistyped the address. Some web addresses are case sensitive"

How can I find out if someone blocks you on Facebook?
Thanks.