c# two object in class dont work thread

c# two object in class dont work thread

this normal working :
private readonly List<Thread> thr = new List<Thread>();
class
public void testthr(object xxx)
{
......
}
button
for (Int32 i = 0; i < textBox8.Lines.Length; i++)
{
var thr1 = new Thread(testthr);
thr1.Start(textBox8.Lines[i].Trim());
thr.Add(threadz);
}
how to ;
public void testthr(object xxx, string yyy)
{
......
}
this class in thread start ?