After finding out that he has a half brother a young man must find his brother and save him from the local gang.

Good start, needs more detail on the main character – right now all we know is that he is a young man. Also needs more detail on what kind of danger the brother is in, is the danger that he will become a criminal, or is his life in imminent danger? Maybe more details on the gang as well? Bikers, drug dealers, fascists, slave traders, child abusers? Etc. Basically make the stakes and goal more clear.

In general, try to be more concise in the wording – “Finding out” can be “discovering”, “find his brother and save him” can be “rescue him from”.