Tsvetkov made his first team debut in a 5–1 Bulgarian Cup win over Maritsa Plovdiv on 7 December 2008, coming on as a substitute for Sandrinho.

He made his league debut on 31 May 2009, again as a substitute replacing Wilfried Niflore, as Litex beat CSKA Sofia 1–0.

[2] He quickly established himself as a regular starter, so it came as a surprise when his contract was terminated by mutual consent in May 2018, several weeks before the end of the season.

[5] On 7 October 2011, Tsvetkov earned his first cap for Bulgaria in the 0–3 away loss against Ukraine in an exhibition match.

He had to wait nearly 6 years to feature for the national team again; on 3 September 2017, Tsvetkov was in the line-up for a 2018 FIFA World Cup qualifier, a 1–3 away defeat by the Netherlands.