With a local vote on the project possibly more than a year away, developers backing the proposed SoccerCity mixed-use development in Mission Valley have launched a new campaign aimed at getting Major League Soccer to hold off decisions on its next expansion teams.

Joined by dozens of young soccer fans and players at a July 24 news conference at San Diego Polo Fields in Del Mar, the investment group that includes La Jolla-based FS Investors and other supporters launched “Wait for SD.”

Proponents including FS Investors partner Nick Stone, project manager for SoccerCity, pointed to supporters’ gathering of 108,000 signatures in 12 days in March, in the initiative campaign that subsequently placed the project before the San Diego City Council.

The council recently rejected a proposal by the mayor’s office to place SoccerCity on this year’s special-election ballot in November, meaning it will likely appear on the November 2018 general election ballot unless officials opt for a special election earlier in the year. Backers said timing issues could cost the city its chance to join the MLS.

“We’re undertaking this campaign on behalf of all the San Diegans who’ve given their time over the past few months to show their support,” Stone said. “We owe it to them to do everything we can to bring Major League Soccer here.”

MLS officials have said the league is scheduled by year’s end to announce the first two winning bids, from among 12 groups nationwide seeking to bring pro soccer to their respective cities. The MLS is set to add a total of four teams, bringing its eventual total to 28.

League officials have previously said San Diego needed to have a stadium plan approved by December 2017 in order to be competitive.

Backers said the “Wait for SD” campaign will include frequent fan events to highlight local enthusiasm for soccer, a social media push to exhibit fan engagement, and contact with MLS officials.