Scratch is a visual, block-based programming language, adopted as a computational thinking development tool in elementary education among many countries. Thailand has also recently included Scratch as part of the computing science course in its basic education. However, Thailand is facing a shortage of ICT teachers who are skillful in Scratch programming, especially in small provincial schools. This research aims to overcome the shortage by developing ScratchThAI, a Scratch tutorial chatbot. It is designed to assist young learners directly through a messaging platform. By giving supports through a textual conversation, more relevant advice, knowledge, and resources could be provided precisely. Different levels of each computational thinking concept are extracted and evaluated by the designed assessment algorithm. Extra predefined exercises are assigned based on the analyzed learner’s strengths and weaknesses in order to actively improving the learner's understanding. Moreover, gamification is incorporated to engage and motivate young learners in computational thinking development.