My chihuahua is dreadful when taken for walks?

[Ali Cop]

Right i got my Chihuahua around 2 months ago, he is now 9 months old, at home he is lovely cuddley lap dog who will play with my other dogs and my parents dogs perfectly at eachother houses. But soon as i him take him for a walk he turns in to like some kind of demond dog he pulls so bad on the lead but soon as he seens another dog i havnt seen anything like it he will growl and snap even if they are like on the other side of the field i have to pick him up and he is still trying to get free to go them. Also another thing is certain people he growls at we can go past big crowds of people and he wont take any notice and one off person walks past and he will snap. Please Help :L