It depends upon the kind of online tutorials you are referring to. I have had experience teaching English using the phone, Skype, and also in a classroom setting. The kind of teaching I did over the phone and thru Skype provided interaction between the teacher and the learner. If you are referring to passive learning thru video tutorials, I can say that they can be effective, if it caters to your learning style. But then, unlike having an instructor or consultant during your study time, you will not receive immediate and guided evaluation. My students who used this medium ranged from 5 years old to the elderly--as in up to 65 years old. Though we have limited time to study, almost all the students provided positive feedback and showed dramatic improvement since their language needs were assessed before, during, and after our sessions.