Raids were being conducted in various parts of Delhi to trace Sahil, the fourth person supposed to have visited the residence of late Bharatiya Janata Party leader Pramod Mahajan allegedly to supply cocaine to his son Rahul.
The raids were being conducted in south Delhi and neighbouring Haryana. A team of Delhi police officials was expected to visit Mumbai, from where Sahil hails, police sources said.
Meanwhile, police were still interrogating Rahul Malhotra, Tishay Khanna and Karan Ahuja, who appeared for questioning at the Mandir Marg police station late on Friday night.
The four persons had allegedly procured drugs for Rahul and late Pramod Mahajan's aide Bibek Maitra.
A lawyer for the three persons claimed that his clients had not surrendered, but were helping the police in investigation.
Maitra died before he could be admitted to the Apollo Hospital, where Rahul is under treatment following suspected drug abuse.
A small quantity of white powder, believed to be cocaine, was found on the person of Rahul when he was admitted to the hospital.
Additional Deputy Commissioner of Police (New Delhi) Manish Aggarwal told reporters that police were interrogating the three people who had turned up on Friday night.
"We are trying to establish the sequence of events that took place yesterday morning," he said. But the three men did visit the Mahajan residence to meet the late BJP leader's son, he added.
Asked about Sahil's background, Aggarwal said his records were being checked.
The additional DCP, however, remained tight-lipped about the suspect drug angle to the episode, saying the white powder recovered from the scene was being examined by forensic experts.
"The CFSL report (on it) is awaited," he remarked when asked persistently whether the powder was cocaine.
Also, police have made no arrests so far, he said adding, the trio was still being interrogated.