Welcome to the forum!
Are you on Metro PCS, or who is your carrier?
A quick Google search brought up a number of guides. You should be able to use Towelroot, which is one of the easier methods of rooting. Here's a link for your flashing pleasure. How to root LG Optimus L70 MS323
Make sure you follow the directions to the letter and you're on the correct OS version before starting. (Not to mention backing up all relevant data, contacts, etc)
Sorry to hear about your rooting troubles. Unfortunately I'm not very familiar with this particular device, but if you could explain what happened when you attempted these root methods, we may be able to steer you in the right direction. Without any detailed information, we have nowhere to start.
Towel root- "This phone is not supported". SuperSU- "SU binary out of date! Please dowload the latest release"- no source given. So on so fourth. Also some of the other rooters i've tried are in japenese or some other foreign language so I can't say what it says because I can't read the damn thing.
Last I checked you should be (per the XDA Towelroot thread) side loading SuperSU via their website as they have the latest updated binaries. (Not sure if the Play Store version has been updated since I last used it) on top of that, if it's telling you your device isn't supported, that's a good sign to not even try. (Let alone root apps in a foreign language you can't understand) just sayin
Good luck and let us know if FBMs link works for you.
Also....Can you tell us what you're looking for with root? People root their phones for many different reasons, so if we can't find a method that works for your device, but we know WHY you want to root, we could then provide you with some alternatives and perhaps third party options that will work just as well.
Hang in there!