How do I ask for forgiveness from people that:
1) I no longer am in touch with
2) Are famous, i.e politicians or celebrities I have looked down upon
3) Professional people who in which asking them for forgiveness could create awkwardness and possibly tension i.e doctors, teachers

And if I ask for forgiveness from those I have hurt or spoken badly about, do I have to tell them what I said or can I just send a general message to them asking for their forgiveness for any wrongdoings I might have committed that could have affected them.

As for 2) you do not need to seek forgiveness from.

As for 1 and 3 if it is not possible to contact them then there is a form of sadaqah called Radd al madhalim. It is taken out with the intention of penitence for the wrongdoing one has done to others and is no longer in contact with.

Similarly the ones who you can contact you can just send a general message asking for forgiveness whilst keeping in mind the thing you said or did.