If you knew someone to be a sinner (fornicator, adulterer, drunkard, homosexual, etc.) would you advise to avoid that person?
It would very much depend on what that contact consisted of and for what purpose you were in their company.
You don't give any background here.
Is this a work situation?
Are you seeking pleasure form the company of these people?
Are you endeavoring to turn them to Christ?
Why did you ask the question in the first place. IF?