The call was one of five recommendations issued by Tunisian civil society "to ensure the success" of the looming vote, according to a joint statement issued by Mourqiboun, the Islam and Democracy Center, Awfiya', Shahed and the Youth without Borders organizations.
"Young people are strongly encouraged to participate in the run-off vote," Monzer Hamdi, a spokesman for the Youth without Borders campaign, told a Tuesday press conference.
The first round of presidential elections in late November, along with parliamentary polls held one month earlier, saw weak turnout on the part of young people, who account for roughly 60 percent of the country's 5.2 million eligible voters.
Observers attribute the low youth turnout to the fact that key demands articulated by young protesters during Tunisia's 2011 uprising – including reduced unemployment and job creation – have yet to be realized.
Next Sunday's runoff will see two candidates vie for highest office: the Nidaa Tounes party's Beji Caid Essebsi, who clinched some 1.9 million votes (39.4 percent) in the first round; and interim President Moncef Marzouki, who won roughly 1.1 million votes (33.4 percent).
The runoff will be held on December 21 inside Tunisia and on December 19, 20 and 21 at voting stations abroad, electoral commission head Shafiq Sersar said at a Monday press conference.
Preliminary results will be announced at midnight local time (22:00 GMT) on the same day as the polling.