I have no problems getting kills on Shen (toplane), but it is tricky. I can already tell you're using the wrong runes for maximum potential though.
Here is my most used Shen page:
9 x AS marks 15% AS
9 x armor seals 9 armor
9 x greater magic resist per level glyphs
3 x health regen quints
Masteries:
recovery
tough skin
runic armor
perseverance
swiftness
grasp of the undying
fury
feast
vampirism
bountyhunter
This offers a insane lane sustain, while still providing some stats for lategame. I usually never have to use the pot that comes with the dorans shield.
Core items: Sunfire cape (even against champs with magic damage I tend to rush this first) it is the power spike item for Shen.
I've long stopped using items like Thornmail/ninja tabi unless theres at least 3 adc's, in favour of deadmans plate for chasing potential. I also use boots of swiftness with alacrity, why? Because if they blow their CC on you, they aren't blowing it on your carries (chances are you already taunted anyway). I usually only get a single AS item and most of the time its triforce/wits end. I think titanic hydra is great on Shen, but only as a final item. Try to get as many items that offer defensive stats, but offer a chunk of HP as well. This increases your defenses, but also your offenses (Ki-strike,Grasp) end game you could be looking at a whopping +400 damage.
Getting kills:
I personally always use ignite, Shen has very little kill potential without it and depends on his opponents making a slip, however if you play smart you can easely rack in a early kill without having to spend it. Farm minions wait for grasp of the undying and ki-strike to both be up, throw Q AA back away into your minions and continue farming. Chances are you dealt a chunk of damage with taking little to none yourself, keep playing aggressively but make sure you stay near your minions so that any retaliation has a chance of pushing the lane towards your turret. If you stall or are actually gradually pushing, you will get a larger minion wave at some point. The instant they are trying to last hit that cannon minion, you taunt them into the entire wave. Don't blow ignite yet, see if they burn flash or try to trade first. If they get low enough, throw in a ignite (or if they were already low). I think it speaks for itself that taunting people under turrets works wonders. I can usually get a 2 to 3 kills in lane before having to B, depending on what champ my opponent plays. Half of the time first blood is mine.
Hope this helps.