Well there isn't any way to tell who the leader is anymore. I'm clan leader and I'm not able to see that I'm clan leader from my Gf's account.
Also there isn't any way to get back the leadership without Asking the person back for it. Support won't do anything to help out. This is a issue that came up a lot in the past. (players accidentally pass leadership to wrong person & can't get it back, etc..) You will have to try and find out who the leader is by asking other clan members then ask that person to pass back the leadership.
Go to the clan page in the game. The leader will be the only one with the clan tag showing next to their name.
On PS3 in a loby, hit triangle like you are going to invite someone to the lobby. Hit the right arrow over three times and it will show you all the members of the clan. Only one will have a gold clan tag to the left of their name.