The 25-year-old joined the Shrimpers in the summer after a trial, having not played a first-team game since November 2014 while at Blackpool.
The former Newcastle and Swindon forward has since scored twice in nine Southend appearances.
Phil Brown's side are undefeated in any match Ranger has started, winning five and drawing three of the eight games.

It has been predicted more than 100,000 fans could arrive in a city with a population of less than 40,000.
"We hope the suggested figures are not the same as the actual number of fans who will turn up," Sylvain Robert told the Sport Wales TV programme.
"I don't know how we'd find space for 100,000 people."
Robert says he and the city's officials are "working on all possible scenarios" and a 10,000-capacity fan zone will be set up.
He added: "We are apprehensive about the number of fans who could arrive without a ticket as it's a problem for this type of event."
According to Paul Corkrey of the Welsh branch of the Football Supporters' Federation, Lens' Stade Bollaert-Delelis "is one of the best stadiums in France".
He added: "But the problem is that's all that's good about it.
"The fan zone is very small. To have a tournament of this size there is strange because there are not many amenities there for supporters. I wouldn't go there."
Robert is worried that the town's reputation may be damaged by the tournament.
"It's not that we would be happier to have fewer people, it's that we would be happier if we can host fans in good conditions," said the mayor.
Uefa responded with a statement, which read: "The host city of Lens, in close collaboration with the local authorities and Uefa, will be implementing appropriate measures to ensure that all visitors enjoy matches in a safe and festive atmosphere, be it at the stadium, in the fan zone or in the city centre."
Watch Sport Wales, BBC Two Wales from 19:30 BST on Friday, 6 May and later on demand and on the BBC iPlayer.

The reigning champions were knocked out after losing 1-0 to Morocco.
The Frenchman's decision to resign after 18 months in the job was announced by the Ivorian Football Federation (FIF).
The Elephants failed to register a win in Gabon, after draws with Togo and DR Congo and the defeat to the Moroccans.
The federation's statement praised Dussuyer's "professionalism, commitment and human quality", adding that "the appropriate measures will be put in place to find his successor".

The National Highway Traffic Safety Administration's Mark Rosekind criticised FCA's recall of 11 million cars and handling of fatal accidents.
He told a hearing in Washington of failures to inform owners of recalls, delays in repairs, and not doing work.
Fiat said it "learned from [its] mistakes and missteps".
The recalls cover Jeep, Dodge, Chrysler and Mitsubishi vehicles from model years dating back to 1993.
Much of the testimony in the hearing focused on a recall of 1.56 million older-model Jeeps with gas tanks mounted behind the rear axles.
The tanks are vulnerable to being punctured in a rear crash. At least 75 people have died in fires involving the Jeeps, according to the NHTSA.
"There will be action," Mr Rosekind said. "What you've heard here is that there's a pattern that's been going on for some time."
He did not detail the sanctions, although they could be a mixture of fines and orders to buy back or replace vehicles.
The NHTSA has yet to decide whether to forward the case to the Justice Department for possible criminal action.
"Recall execution is where we have fallen short," said Scott Kunselman, FCA's senior vice president for vehicle safety and regulatory compliance in North America. "We have learned from our mistakes."
Southend United striker Nile Ranger has signed a new three-and-a-half year contract with the League One club.
[NEXT_CONCEPT]
The mayor of Lens says he is apprehensive about the number of supporters expected to visit when Wales face England at Euro 2016 on 16 June.
[NEXT_CONCEPT]
Michel Dussuyer has stood down as Ivory Coast manager following his team's early elimination at the Africa Cup of Nations.
[NEXT_CONCEPT]
Fiat-Chrysler Automobiles (FCA) faces action over the mishandling in the US of car recalls, the country's top vehicle safety regulator has said.