A group of about 20 used social network sites to get together to help look for the 16-year-old, meeting at the Plymouth side of the Tamar Bridge before crossing over the river to Saltash in Cornwall.
Jordan, from Plymouth, has not been seen since he jumped from the Torpoint Ferry into the River Tamar as he headed to a new year street party in Torpoint with a group of friends.
The emergency services resumed their own searches today but admitted that it was likely they were looking for a body.
Detective Inspector Nick West, of Devon and Cornwall Police, said: "We always keep our options open but practically, looking at the temperature of the water on the night, the flow of the river and the way he went into the river, it is probably unlikely that we will find him alive."
West said he was keeping an "open mind" to why Jordan decided to jump from the ferry.
"We certainly have not had anybody come forward and say this is why Jordan jumped in the river," he said.
"As far as we know it was a group of 16-year-olds who were going out to enjoy a night in Torpoint with a street party, and 70 metres from the riverbank something has happened on the ferry and Jordan has decided he is going to jump into the water.
"The river is very fast flowing and at the moment Jordan hit the river he probably became overcome with shock.
"Whether it is a prank or not, I don't know at the moment but I suspect as time goes on it will be something like that and unfortunately it has gone very tragically wrong."
The detective said officers were supporting Jordan's family.
"His family are very upset and distressed," he said.
"We are supporting them with police officers to make they are provided with updates. We are just trying to do our best to support them through this horrible time."
Police met Jordan's friends earlier and advised them of the dangers of entering the water.
"We wouldn't encourage people to go looking in certain areas of the River Tamar as it is a very dangerous place and some of the mud banks are very loose and people could get trapped by the incoming tide," West said.
"We have met with the group today at the Tamar Bridge and we welcomed their support and appealed for them to give us any information about what might have happened to Jordan.
"We asked them to be mindful of the fact it is a dangerous river and not to enter the river at any time and if they see something that they think is of interest to the police, give us a ring and we'll come and do our best to deal with the situation."
The emergency services were taking advantage of the high tide to get as close as they could to the river's edge.
"We'll carry on as best we can with the assistance of the RNLI and the coastguard and the Ministry of Defence launches today," West said.
"As private boats are out and about on the river they will be aware that Jordan is still missing, so we ask them to keep an eye out.
"Tomorrow the search will be reconvened and we'll check the same areas again, and because of the significant tidal changes we have in the river, he could be anywhere, really."
Friends of Jordan took to social networking sites to pray for his safe return.
Savanah Rich appealed on Facebook for anyone with information to come forward.
She said: "Never give up hope. I will search day in day out until I find you Jord.
"I have total faith that your (sic) still out there somewhere, hate being depressed, being sick and deprived of sleep but I'm not giving up on you just yet! Love you so much."
Fletcher Medlen wrote on Facebook: "Jordan you mean the world to me your my best friend and you always will be I f****** love you Jordan Cobb."
Matt Lethbridge tweeted: "Happy new year people but thought are with Jordan Cobb. Praying for you my man."
He later added: "Going sleep hoping to wake up to good news about Jordan Cobb. Thoughts are with you mate."
Lauren Prend tweeted: "Praying for Jordan Cobb to be safe, can't believe what's happened to him. Wasn't that long ago when I spoke to him! Love you Jordan xxx"
Jeorgia Best tweeted: "Hope Jordan Cobb is okay :("
Katey Northcott added: "Thoughts go out to Jordan Cobb and his family hope he's alright. xx"
The Torpoint Ferry, which is pulled across the River Tamar on chains, is one of the main ways to travel between Devon and Cornwall and was established in 1791.