There are plenty of chess tactics trainers online, to improve your chess skills, but I cannot find a single one for go. Is studying tactics useless for go?
On the contrary, studying tactics for go is essential. Books or online resources on Joseki, Tesuji, and Life and Death situations are good places to start, followed by general opening strategy as you gain experience.
Playing games on 13x13 boards as well as the standard 19x19 will assist you in gaining experience in the balance between influence to the centre and territory along the sides and corners.
However, programming go is considerably more complex than programming chess, leading to fewer good trainers available.
Go tactics are essential, as other answers have said. Two critical aspects of beginning Go play are fuseki (openings, similar in theory to chess; you want to position your first pieces to stake a claim and assert control over territory on the board that you will then defend) and joseki (tactical "battles" for a section of the board; various combinations of white and black stones can be played in a wide variety of ways that boil down to a lesser number of "best practices" that should be studied).
However, as with almost any pursuit, a good player knows the unwritten rules and how to follow them, but a true master knows which of those he can break, and when. You might make it to single-digit kyu just by studying joseki, but the mark of a true dan-rank Go player is an intuitive knowledge that he doesn't have to play the joseki exactly as he's memorized, if he sees an alternate play based on the surrounding stones that would create an advantage that doesn't exist in the smaller, more sterile joseki studies.
As far as joseki/fuseki resources, there are tons of online resources; Google those terms and you'll find websites/apps that teach you various aspects of these tactical battles.
The best way to study Go tactics is to do lots of problems. GoGrinder is a really good way to practice if you're using a computer or an Android phone. I haven't kept the iPhone version up to date, so I can't really recommend that anymore.
In chess, there are a handful of maneuvers such as "pins, forks, hurdles, discovered checks, etc. that are grouped under "tactics."
In Go, there are whole subcategories of tactics such as "Life and Death," (self explanatory), "tesuji," (literally "sleight of hand"), endgame tactics, etc. Each of these subcategories has whole books devoted to them, and improving in even one category will substantially raise your overall strength.
So, unlike chess, you don't study "tactics" as a group, but rather individual categories of tactics.