Hi I'm sort of new to the cs:s community (played about 30 hrs or play) and had a few questions. 
 
1) Does silencing the m4 cause you to now show up on enemy radar? 
 
2) What effects does silencing have on the gun?

1) You show up on your enemy's radar when you have been spotted so silencing your weapons doesn't make you show up on the radar.
2) Silencing your gun changes the recoil/spread of the gun and obviously makes it quieter. I'd say it's mostly a matter of preference.

I don't know if it stops you from showing up on the radar, but I have noticed that the gun gains a little bit more recoil. 
 
That said I never use the silencer. I don't sneak around often.

I heard that silencing the gun reduces the damage a bit, but also the recoil. 

The only difference is the model/skin, it doesn't effect the guns performance at all. It is a preference thing. The only thing you'll gain is a quieter gun, which can be a benefit, since sound is so crucial in counter-strike.

Less damage. It's what separates noobs from pros.

There are quite a few varying beliefs as to what the silencer does; I can confirm that the silencer reduces damage by a very small amount (I think this is mostly due to a slightly slower firing rate). Some also argue that the silencer increases accuracy (some even say it decreases it). All I can say is that it becomes a personal preference: some players use the silencer, others don't.
 
Source: Over a decade of CS experience.

Pros:
It makes it sound super bad-ass and quieter.
Cons:
More recoil (burst shooting the M4 is crazy accurate anyway)
 
 I would advise using it under stealthy circumstances.

silencer changes accuracy but lowers damage. 
 
take for example the silenced USP...takes like 3-4 in the head to kill :P 
 
 if you spray and pray, i say dont put it on, make it loud Rambo style :D

Use the silencer. I've found that it makes the gun more accurate, and the noise is harder for enemies to pinpoint.

I use a silenced M4, you appear on the radar if you are spotted, its nothing to do with silenced weapons.

its not less direct damage, unless through walls