The invite option you have on the profile. Just go to their profile and you'll see the option invite.
"Peace cannot be kept by force; it can only be achieved by understanding" - Albert Einstein | "There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle” - Albert Einstein | "Learning by making mistakes and not duplicating them is what life is about." - Lindsay Fox | "Everyone makes mistakes in life, but that doesn’t mean they have to pay for them for the rest of their life."