There are Google+ directories popping up every day. Unfortunately, while Google+ is still in beta, you may or may not find people high up in companies with whom to connect.
The good news is if you're in Google+ right now, it's because someone invited you. Check out your friend's friends. There isn't a requirement for new members to list their employer, but if they do (and if they give you access to it) you can see it.
Use the built-in search functions to see who you are connected with indirectly. You never know when a connection exists that may be useful to your search. Always ask for the introduction after you've discovered the connection.