I would think from my own point of view, witnessing is one on one, evangelizing is towards a crowd, just my thoughts
Evangelizing is something that you do, i.e. It is proclaiming the good news (the message of the gospel) through some media. Witnessing is who you are, i.e. A living sacrifice dedicated to serving God and His creation. Witnessing takes place in every moment of your life, at home, at work, when traveling, when meeting with people. Witnessing is also the way you live, ie. How you do life. It involves how you handle problems, serve others, deal with disappointment, and put your ego aside to glorify God when you are successful. The way you evangelize shows the kind of witness that you are. You may be humble or proud, you may be Christ centered or church centered, you may be interested in transformational change in those you evangelize to, or you may be interested in numbers for your scorecard.
When we witnessed, our purpose and aim is to bring our audience to believe and accept our report, in order to make them what our testimony has turned us to be.Therefore, witnessing and evangelizing is more or less the same thing.