Should I have kept betting?

Party Poker 1/2 Hold'em (10 handed) converter

Preflop: Hero is MP1 with [Kc], [Kh].
3 folds, MP2 calls, MP3 calls, Button calls.

Flop: (17.50 SB) [8c], [4h], [9d] (4 players)
Hero bets, MP3 calls, Hero calls.

Turn: (14.75 BB) [2h] (3 players)
Hero bets, MP3 calls, Hero calls.

River: (20.75 BB) [3s] (3 players)
Hero bets, MP3 calls, Hero calls.

Final Pot: 26.75 BB

Whats the other raiser like?

Just sat at the table, 2nd hand.

MP2's betting pattern says he can beat an overpair. I don't know what MP3 is doing cold calling all of those raises. You could check/call turn and river.

Just Check/call the flop.
I smell a set

if he is unknown, shut down, and just call down.

Slow down after the flop cap.

Can't wait for the results on this one...I smell comedy gold from MP3.

Results in white below:
Hero has Kc Kh (one pair, kings).
MP2 has 9s 9h (three of a kind, nines).
MP3 has Js Jc (one pair, jacks).
Outcome: MP2 wins 26.75 BB.

You mean c/c the turn, right?