So you need clearing this up? Here comes.
If a pokemons attack does 0 damage (like Call for Family) and has Plus Power attached to it, the attack still does only 0 damage.
Why? Because it says on the card "does 10 more damage". If there in nothing to add to, you can't add it. In pokemon, 0+10=0. If there would be something to add to, like in for example Tackle 10, you do 10+10=20. This is writen in the pokemon TCG core rules.
Here is a part of Darkness energys ruling for example...
Q. The wording on Darkness Energy from the EX:Ruby/Sapphire expansion says, "if the Pokémon Darkness Energy is attached to attacks, the attack does 10 more damage to the Active Pokémon" Does this mean that you get to add +10 even if an attack does no damage at all to the Defending Pokémon (i.e. EX:Sandstorm Murkrow's "Surprise" attack)?
A. No, it still applies only if there was initial damage to add to. So in other words, you still have to do some damage in order to have "10 more" done. (Sep 18, 2003 PUI Rules Team)
EDIT: And if that's not enough for you, I went through the trouble to find an official PUI rulings team answer for you.
http://pokegym.net/forums/showthread.php?t=58914