Spearmen works absolutely best in relatively large units 30-50. Give them at least two detachments to support them.
I run them six wide against all but 40mm monstrous models to capitalize on the spearmen strengths. Spearmen are exceptionally good against low points cost tarpit units. You get a reasonably amount of kills and will break them pretty fast since you have lots of ranks.
In my opinion you should buy them a shield because if you bring spears you might as well capitalize on their defensive abilities. There are spells that you can use to capitalize on this, such as reducing the strength of your opponent, increasing your armour save, re-rolling armour saves, Mindrazors etc.
In my opinion you should bring at least one Lv2 shadow wizard if your core troops are Spearmen. Metal is also god where you can give them extra armour save and the armour piercing ability. Shadow is also very useful for your missile and artillery if you get access to that toughness de-buff spell.
Some other general tips of mine....
Put a defensive character in the corner of the unit, that way he will soak up some attacks from the enemy. You could also issue a challenge and with that more or less block some models attacking your character. Another tactic of mine is to kill the enemy unit champion (with Hochland rifles) and force the enemy uber killer character to attack my tank Character, thus reducing the number of attacks on the spearmen unit.
I have won a few fights this way against hordes that seemed more or less unbeatable at first glance...
