Yes, you can go for the rank of Team leader if you do not have a team. You are not prohibited. You may have a downline no matter how few which you should nurture, and probably have been nurturing through your weekly posts and maybe one on one communication.
The ideal situation however, is that you should have a Team, to properly earn the tag Teamleader. This you do through sustained recruitment, training and retetion of affiliates. Duplication is a name of the game.