What are the tactics used by teams in the mobile version of Agar.io?

It's a bit more complicated.

Of course, the main thing it's not to eat each other unless an 'enemy' bigger come to eat the whole team. In that case the best thing to do as a team is give enough mass to the bigger one of the team to prevent the bigger one to eat the team. Eventually, if partners get small enough, it's better if the leader eats them that if any other small cell passing by does.

The tactic as a team it's to have a leader, a bigger guy, that guy will be the eater. The remaining partners of the team should eat the little ones near the leader and then give mass to the leader so he can eat larger cells and give back mass to the partners. With this tactic there will be a point where the little partners would be large enough to eat pretty big cells (like leader being top 1 and partners near top 10). When you reach that point, you can fight other teams, how? You have some options here:

1) When the other team approaches, the partners divide themselves as many times as needed and give their parts to the leader so he can divide and eat the other teams leader.

2) You can go instead for the little partners (not too little now, remember) to prevent the enemy leader to get bigger. Just remember, your leader, to avoid to be eaten, has to be at least bigger than 1/2 of the enemy leader. If not, the enemy leader will just split and you and your team are done.

3) Keep eating smallers guys, with your leader always facing the enemy leader and partners, this way, the leader protect its partners while they are getting big enough to go to point 1) or 2).

Just remember this too: > Size = < Speed. So if you are ocasionally smaller than the other team, as long as you don't get in a corner, you'll be safe.

Hope this help.