How do you recruit players openly in state chat?

You can ask for new members in the state chat. You can also see if any of those posting have an alliance tag or not. (tag is next to the names). If they don't have a tag then you can tap the message and send them an alliance invite. (you will need to be R4 or above I believe)

In either case you can tap on the players avatar image and send them a private message to ask them if they want to join you.