You can say, "there's a person" (meaning "there is" a person)
Or
"There WAS a person" for a past-tense situation.
For your sentence, "there's" OR "there is" would both be correct.
"There were" - this would only be used for more than one person.
I.e. "There were people at the bar that I didn't want to talk to. At the concert, there's a man I want to meet."
I hope this helps =O)