What those the particle ら mean at the end of a verb in japanese?

Question:

I've seen it a few times in japanese texts and i can't understand it. What's worst is that i can't find any information related to that on the internet. Please can you explain generally the uses of -ra at the end of a verb in its differents forms?

Just to put an example i saw a japanese add (all written in hiragana), that said:みんなでがんばろら. What does this mean?

Answer:

It's more like slang, just an extra add on. Informal talk.

EDIT: The whole text, says something like "Good luck everyone." or "Everyone should do their best."

みんな - Everyone
で - (Connects the sentence)
がんばろら - Slang for good luck, or to do your best. The formal term would be がんばって

There is no actual meaning for -ra. There are just some words that they turn informal by adding on and taking off endings.