Perhaps you should ask him his reason. Until you know that reason, helping him will prove difficult.
I’m guessing, but, if he is a single person, one possible reason might be that some single people often feel uncomfortable going places by themselves where other people go with family and friends. If this is the case for your friend, explain to him that Mass is not a social event. It is a grave obligation for Catholics to attend Mass on Sundays and holy days, whether or not they can do so with family or friends. He might even try looking at the bright side: Attending alone means that he will not have to be distracted by the needs of others for whom he is responsible (e.g., small children). He can focus himself entirely upon Christ and upon Christ’s sacrifice that is being sacramentally re-presented on the altar.