Guppys Missing Tails Due To Nasty Fish!

[Disconfigured]

Is it similar to the other guppies tails? It would be good to check the water parameters (pH, ammonia, nitrite, nitrate) if you havn't already.
A picture would be good as well but I know you're having trouble. Have you tried uploading to photobucket and then linking the pictures here?

The other one, the blue guy, has lost more of his top fin but no more of his tail. the red one, who's tail is now seriously damnaged hadn't lost much at all.
I'm having to reduce the picture size so they're not coming out very clear.

 

[Freedom]

I feel for these guppies.  You suspect the platys are attacking them, but you haven't moved any to another tank. 

 
Platys beat up the male betta I rescued.  When the tank is too small, even community fish will be stresssed and fight.

 

[Disconfigured]

I feel for these guppies.  You suspect the platys are attacking them, but you haven't moved any to another tank. 
 
Platys beat up the male betta I rescued.  When the tank is too small, even community fish will be stresssed and fight.

I have never once mentioned or thought the platys are attacking. The Betta I had in the tank was attacking, he's gone. I've had the platys with the guppies since day 1 and they have only ever been friendly.

 

[Mamashack]

It seems you have been the victim of bad advice from the pet store. They tell you enough to get you to buy in the first place and then when it all inevitably goes pear-shaped you go back for either medications for them when they become diseased or replacement fish for the ones that have died. A lot of us have been in the same situation. Don't beat yourself up, but do learn from this.
Always do your research before going to the LFS and then you'll have the knowledge to buy appropriately. In other words never buy on impulse, buy with your head and not with your heart. Get fish you can easily provide the right environment for.
I had platies in with a betta once (in a 60L tank) and they fought like mad, both the betta and the male platy had torn fins so they were both as bad as each other.The platies are, as previously said, in far too small a tank and that eventually leads to stress and fighting even in the most peaceful of fish under normal circumstances.

Forgot to add that if the injured tails have white edges it could be fin/tail rot and will need treating before the fins/tails disappear altogether and start to infect the body of the fish with potentially fatal results.
I say this not to frighten, but so that you can ascertain whether it is fin/tail rot because it is contagious and could affect all the tank occupants under these stressful conditions.

 

[Paradise3]

You have a Bristlenose pleco which will reach about 8 inch maximum(commonly max out at 6) so will need a bigger tank(30inch bare minimum, 3ft is much better).
Platies do need a bigger tank than 22l unfortunately as they can get pretty chunky.
Guppies are fine in a 22l tank.
And the loach has already been discussed