Do other pokemon use the move round to get it to do more damage or does it have to be used more than once?
Using. So use Round, switch to a different Pokemon, and use it again.
Round inflicts damage, which will double in power to 120 if used consecutively by an ally and definitely will be used by the ally directly after the first user, regardless of speed.
http://bulbapedia.bulbagarden.net/wiki/Round_(move)
Other Pokemon have to use it. Lets say you have Altaria and Duosion. Both use Round. Altaria will attack with a 60 BP Round. Immediately after, Duosion will attack with a 120 BP Round.
>...does it have to be used more than once?
This is Echoed Voice.
it only works in THE SAME TURN. therefore, it's added effect only works in double and triple battles. Send out multiple pokemon with the round attack. Use round once, and both/all 3 will use it in the same turn, increasing in attack for each pokemon