Is it written anywhere in the rule book whether you could use a touch spell on multiple targets?

For instance is it possible to hold out your hand and then have the rest of your party grab a finger or touch a piece of you and then cast increased reflexes or something on all of them simultaneously?

And then you'd only need to sustain 1 spell on N targets and the entire party would have increased reflexes?

It sounds very good and obviously would be extremely difficult to perform on an enemy, but on allies this would be a piece of cake.

I haven't seen this discussed anywhere.

Furthermore if this is not allowed for whatever reason, then has any GM ever allowed LOS or LOS(A) health spells?

There is some fluff that argues against it, but at least in Street Magic I see nothing that explicitly states that it is not possible.

Again for instance LOS(A) version of increased reflexes that can be cast and sustained on the entire party?

The texts of the spell descriptions tend to be pretty specific about single or multiple targets, regardless of whether it is a touch spell or some other form. So for example, the Increase Reflexes Spell says "a voluntary subject."

You could develop your own, multi-target version, but expect the drain to increase as it does in other single-to-multiple conversions.

I agree you can multicast touch spells (following all appropriate penalties and modifiers of course).

like wise you could cast multiple spells in an action like normal, but you'll be splitting for each spell.
I have been kicking around making a multiple target death touch spell.
which i think the drain would be the same as manabolt in both 3ed and 4th

It explicitly states that all Health spells are range: touch.
There are fluff justifications, but it boils down to a balance justification.

To 'Heal' someone you must touch them and
remain 'in range' sustaining it until the spell 'becomes permanent'.

Also, spells not explicitly listed as area are single target spells.

You could multi-cast, splitting your dice pools amongst the targets.

Surely, some GM somewhere has broken or altered every rule in the entire system,
so you might want to talk to your GM.

The cardinal rule in gaming is have fun, so talk it out.

I'd say you could split your dice - just like in Melee - and there is a dice penalty for touch attacks