If your friends don't have Surf, you can send them an invitation to Surf using any of the messengers available on your device. Your friend will receive a link by opening which he will be offered to install Surf. It's faster and more convenient than asking them to manually find and install Surf through the app store.
To invite a new user to Surf:
On the main screen of the application, tap the icon with the human to open the contact book.
On the Address Book screen, tap Invite friends.
Enter your friend's name in the input field and tap Share a personal invitation.
In the opened window, select the messenger and chat through which the invitation will be sent and confirm sending.
If your friend already has Surf installed, then the link he received will open a chat with you, in which he can chat with you.