Incomming requests should show up in Notifications.
Tap the Home button, chosing Circles, then the People tab. The should be a Suggestions choise. This is the only method I know of to send a rquest via the mobile site. There is a search function, so it might be possible to search for someone you know.
The mobile site is very limited. The app for the iPhone only slightly less so. Any attempt I make to go to the Desktop site in Safari crashes.
I'm far from a Google+ expert, so someone else may have a better answer.