Wasn't it 逃げよう (with the last vowel elongated) that you actually heard?
Then that's what's called the volitional-form of a verb. You can create it by replacing the last る with よう for vowel-stem (aka ichidan or ru-) verbs, or by replacing the last u-vowel with the o-vowel equivalent and adding う for consonant-stem (aka godan or u-) verbs. Its primary meaning is "Let's ~" and "I'm going to ~".
The sentence-end particle よ (as in そうだよ, 楽しいよ) has nothing to do with the volitional-form. (It doesn't end with よ in the first place.)
In fact there is also 逃げよ (without the elongated vowel), which is the archaic imperative form of 逃げる (which was 逃ぐ in classical Japanese, strictly speaking). The meaning is "(You must) escape!" This is much more rarer and never heard in today's ordinary conversations. But you may occasionally hear 逃げよ from a stereotyped pompous noble person, a ninja, a samurai, or a 1000-year-old demon in various fictional works.
EDIT: @kroki's comment reminded me that 逃げよう can be sometimes shortened to 逃げよ in very casual conversations. Casual/colloquial ("let's") 逃げよ is pronounced as にげよ{LHH}, whereas the archaic/pompous/literary 逃げよ is pronounced as にげよ{LHL} (like にげろ{LHL}).