Vergne and Ricciardo scored only a handful of points in 2012 with the STR7 as they struggled to break into the top ten.
"Naturally, we will be expecting more from them this year as they both tackle their second full season of Formula 1. However, we are well aware it is up to us to provide them with a car that’s capable of allowing them to show their undoubted talent," he said at the launch of the STR8.
"Until we all line up on a real race grid, there will be no clear picture of what we can expect. Nevertheless, we have set ourselves a target of finishing sixth in the Constructors’ classification," he added.
STR slipped to ninth in 2012 and have finished in the top six only once in their seven year history, when they finished sixth in 2008.
Technical director James Key, who joined the team in September last year, hinted that a lot of the team's 2013 efforts will be poured into the 2014 car.
"The major technical regulation change coming in 2014 is having an impact on us already and will do throughout the coming year," he said. "Every team faces this challenge, regardless of size, but it has a bigger impact on the smaller teams: we are looking at a completely different car so you cannot carry over many established designs or philosophies from 2013 to 2014."
"We will have to build up our knowledge of the new regulations and their implications significantly and apply it to the design of the 2014 car. It’s a balance between being as competitive as possible this year, while being well prepared and competitive for 2014 and beyond, but that’s the nature of the business and a great challenge.
Tost also confirmed that Steve Nielsen, formerly of Renault and Caterham, has joined STR as their team manager.