Is приятель not as close/familiar as друг? If we have someone we know but not close enough to be called a friend (or pal, mate, buddy etc... these are all friendly forms), then "acquaintance" is probably the best option. You know the person, but not closely.
If it's from a work situation, use "colleague". If it's someone you only talk to for business or getting something done, use "contact". This is probably closer to the meaning of знакомый.