hay

They both have the same meaning, but the phrasal verb "meet up" has a slightly more casual feel to it. The "up" part suggests a desired result, in this example. Compare "chat / chat up", "cook / cook up", and so on. Warning: this meaning I attached to "up" certainly does not apply to all phrasal verbs which use "up". You'll get the proper idea by seeing the phrasal verb in context. Stay flexible.

They both mean the same.