The Teesside club lost to Norwich in the Sky Bet Championship play-off final at Wembley last season.
Karanka has identified a new striker as key to mounting a new challenge this year but has been frustrated as Blackburn Rovers continue to reject bids for Jordan Rhodes.
“Jordan is an amazing player, but Jordan is not the only one on our list,” he said.
“We know our problems last season and the previous season and it was that we didn’t score enough goals to get promotion and we need to strengthen our squad with a striker and Jordan is one on the list but we are working in other ways.”
Karanka revealed that Crystal Palace striker Dwight Gayle is also on a list of potential transfer targets.
“He (Gayle) is a striker, he scores goals, another one on our list,” Karanka said.
“I like the good players on our list, they are the best, but we have other alternatives, we have other positions so we are working really well.”