Mikel removed his profile from the social networking site less than 24 hours after his mistake helped cost Chelsea victory in the opening match of their Champions League defence against Juventus.
Chelsea originally insisted it was entirely coincidental that Mikel, who insisted he was entirely unaware of any abuse, had decided to delete the 'Mikel12Official' account he set up this summer. However, the club admitted that they have informed the police after being made aware of the developments.
A statement read: "We've been made aware of racist tweets targeted at Mikel which are totally unacceptable, disgusting and abhorrent.
"We've informed the police and support taking the strongest possible action."
Mikel refused to hide from his mistake after Wednesday night's 2-2 Group E draw against Juve.
The 25-year-old gave the ball away 10 minutes from time before he and his team-mates failed to prevent Claudio Marchisio playing Fabio Quagliarella into space for the equaliser.
Mikel said afterwards: "If I want to make up an excuse, I can. But, for me, I gave the ball away. I put my hands up, we move on.
"I'm sorry about the mistake, but there are no excuses."