You will need to either create the thumbnail yourself (would get old) or use this solution (recommended) as shown here:
Alternative to YouTubes Video API to get video thumbnail[
^]
Thought I would add and example of how this might be done.
e.g.
your video link:
http://www.youtube.com/watch?v=OSUO0Rgfo1w&feature=related
so with this particular video link and possibly all youtube links you could do something like this to create the image link.
e.g.
In C#
string videoLink = "http://www.youtube.com/watch?v=OSUO0Rgfo1w&feature=related";
string imgLink = "http://img.youtube.com/vi/";
string[] temp = videoLink.Split(new char[] { '=', '&' });
imgLink = imgLink + temp[1] + "/2.jpg";
or VB
Dim videoLink As String = "http://www.youtube.com/watch?v=OSUO0Rgfo1w&feature=related"
Dim imgLink As String = "http://img.youtube.com/vi/"
Dim temp As String() = videoLink.Split(New Char() {"="c, "&"c})
imgLink = imgLink & temp(1) & "/2.jpg"
would give you your image link:
http://img.youtube.com/vi/OSUO0Rgfo1w/2.jpg