Prudie is correct. Manquer, in this sense, has the meaning of "to be absent". So, "tu me manques" means "you are absent to me" or, put another way, "you are missing from my life".
And, just for completeness, "je *te* manque" (not "je *tu* manque") means "you miss me" in the sense of "I am absent from your life".
Strangely, "manquer" is often translated in dictionaries as "to miss", but French doesn't usually use that verb where we would say "miss". In fact, the example you have given is one of the few occasions where they do. Much more common is "rater" or "louper"...