Assuming that your velocities are already angular velocities (number of radians per time unit), adding a for loop and a vector to store the points handler should work. I also modified the plot function so to have always the same color of the border and filling of the points. Don't know what you're trying to do, but is pretty hypnotic :)
radius=[10 15 20 30]
velocity=[5 2.5 15 20]
colors=['y','m','c','r'] % This is to just make the points different colors
p=zeros(4,1); %here we will store the handles to delete the point
hold on
for i=1:4 %Loop to create multiple circles
th=0:pi/50:2*pi;
xunit=radius(i)*cos(th);
yunit=radius(i)*sin(th);
h=plot(xunit,yunit);
p(i)=plot(xunit(1),yunit(1),'o','MarkerFaceColor',colors(i),'Color',colors(i));
%creates a point on each graph
end
time=[0:0.001:100]; %time vector in seconds
for t=1:length(time)
for i=1:4 %Loop to create multiple circles
delete(p(i)); %delete the old point
%computes the new angle for each point as velocity*time
xunit=radius(i)*cos(velocity(i)*time(t));
yunit=radius(i)*sin(velocity(i)*time(t));
%creates a point on each graph
p(i)=plot(xunit(1),yunit(1),'o','MarkerFaceColor',colors(i),'Color',colors(i));
end
pause(0.01); %wait 0.01 seconds so the plot is displayed
end
hold off
