The most recent data I have (extracted from the forums) is November 2017:
Lvl Users
01 7849
02 4378
03 3563
04 2474
05 1444
06 1402
07 1223
08 1182
09 1097
10 989
11 948
12 746
13 587
14 516
15 415
16 386
17 404
18 419
19 343
20 340
21 347
22 334
23 264
24 213
25 225
26 193
27 197
28 153
29 123
30 142
31 143
32 90
33 93
34 94
35 70
36 69
37 91
38 83
39 77
40 75
41 72
42 58
43 47
44 44
45 34
46 25
47 38
48 31
49 33
50 42
51 63
52 29
53 39
54 30
55 37
56 30
57 20
58 30
59 18
60 358