You can now challenge friends who play TombQuest to invade your tomb.
To challenge a friend
Load up the TombQuest game. On the homepage, go to Invade > and then on the Invade screen, select the Friends icon (next to Attack History) on the Your Friends panel to view your friends and their tombs. If you click someone's name, you'll be able to send them challenge requests.
To view challenges
You can also view challenge requests that others have sent you. Go back to the Invade screen and select the Friends icon. In the open panel, you'll see a bunch of tabs on the left side of the panel. Select Challenge Requests and you'll see invitations from your friends that you can accept to invade their tomb.