Almost 4year old becoming some what violent for attention! Need some advice!?

My son will be four the 21st of July and as of lately he is hitting his younger sister (age 24 months), taking toys from her, hitting and headbutting me (his mother). He is also grabbing adults faces and forcing them to look at him when they are talking to other people (children and adults)! I'm loosing patience fast because talking to him about what he has done wrong doesn't seam to help! Other punishment like time out don't seam to work either! He seams to have become very defiant to the point of doing things he know he isn't allowed to do (climbing on counters then jumping off them,standing on the table, running out the front door and so much more)! I believe he is doing all of this for attention and I don't know how to deal with all of this so suggestions would be wonderful!